fix(fastify): Add __internal_enableHandshake option to skip handshake flow#8560

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wobsoriano merged 3 commits into from
Sep 1, 2026
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fix(fastify): Add __internal_enableHandshake option to skip handshake flow #8560

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815b7c0
fix(fastify): Add __internal_enableHandshake option to skip handshake…
wobsoriano Sep 1, 2026
386bcff
refactor(fastify): Move stripHandshakeCookiesAndParams to utils
wobsoriano Sep 1, 2026
3823adc
Merge branch 'main' into fix/fastify-runtime-secret-handshake
wobsoriano Sep 1, 2026
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5 changes: 5 additions & 0 deletions .changeset/fastify-internal-enable-handshake.md
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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
'@clerk/fastify': patch
---

Add an internal `__internal_enableHandshake` option to `clerkPlugin()` (defaults to `true`). When set to `false`, the plugin skips the handshake flow and strips handshake cookies and query params before authenticating requests. Intended for API-only backends that cannot return `Set-Cookie` headers to the browser.
147 changes: 147 additions & 0 deletions packages/fastify/src/__tests__/withClerkMiddleware.test.ts
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Original file line numberDiff line numberDiff line change
Expand Up@@ -314,4 +314,151 @@ describe('withClerkMiddleware(options)', () => {
}),
);
});

test('skips handshake redirect when __internal_enableHandshake is false', async () => {
authenticateRequestMock.mockResolvedValueOnce({
status: 'handshake',
reason: 'session-token-expired',
headers: new Headers({
location: 'https://fapi.example.com/v1/clients/handshake',
'x-clerk-auth-status': 'handshake',
'cache-control': 'no-store',
}),
toAuth: () => ({ tokenType: 'session_token' }),
});
const fastify = Fastify();
await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
const auth = getAuth(request);
reply.send({ auth });
});

const response = await fastify.inject({
method: 'GET',
path: '/',
headers: {
cookie: '__clerk_handshake_nonce=deadbeef; __client_uat=1675692233',
},
});

expect(response.statusCode).toEqual(200);
expect(response.headers.location).toBeUndefined();
expect(response.headers['cache-control']).toBeUndefined();
expect(response.body).toEqual(JSON.stringify({ auth: { tokenType: 'session_token' } }));
});

test('falls back to a signed-out auth object when a skipped handshake state has a null auth', async () => {
authenticateRequestMock.mockResolvedValueOnce({
status: 'handshake',
reason: 'session-token-expired',
headers: new Headers({
location: 'https://fapi.example.com/v1/clients/handshake',
'x-clerk-auth-status': 'handshake',
}),
toAuth: () => null,
});
const fastify = Fastify();
await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
const auth = getAuth(request);
reply.send({ userId: auth.userId, isAuthenticated: auth.isAuthenticated });
});

const response = await fastify.inject({
method: 'GET',
path: '/',
headers: { cookie: '__client_uat=1675692233' },
});

expect(response.statusCode).toEqual(200);
expect(response.headers.location).toBeUndefined();
expect(response.body).toEqual(JSON.stringify({ userId: null, isAuthenticated: false }));
});

test.each(['dev-browser-missing', 'dev-browser-sync'])(
'still redirects for %s handshake even when __internal_enableHandshake is false',
async reason => {
authenticateRequestMock.mockResolvedValueOnce({
status: 'handshake',
reason,
headers: new Headers({
location: 'https://fapi.example.com/v1/clients/handshake',
'x-clerk-auth-status': 'handshake',
'x-clerk-auth-reason': reason,
}),
toAuth: () => null,
});
const fastify = Fastify();
await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
reply.send({});
});

const response = await fastify.inject({
method: 'GET',
path: '/',
headers: { cookie: '__client_uat=1675692233' },
});

expect(response.statusCode).toEqual(307);
expect(response.headers.location).toEqual('https://fapi.example.com/v1/clients/handshake');
},
);

test('strips handshake cookies and query params before authenticating when __internal_enableHandshake is false', async () => {
authenticateRequestMock.mockResolvedValueOnce({
headers: new Headers(),
toAuth: () => ({ tokenType: 'session_token' }),
});
const fastify = Fastify();
await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
reply.send({});
});

await fastify.inject({
method: 'GET',
path: '/?__clerk_handshake=token123&__clerk_handshake_nonce=nonce456&foo=bar',
headers: {
cookie: '__clerk_handshake=token123; __clerk_handshake_nonce=nonce456; __client_uat=1675692233',
},
});

const [req] = authenticateRequestMock.mock.calls[0];
expect(new URL(req.url).searchParams.has('__clerk_handshake')).toBe(false);
expect(new URL(req.url).searchParams.has('__clerk_handshake_nonce')).toBe(false);
expect(new URL(req.url).searchParams.get('foo')).toBe('bar');
expect(req.headers.get('cookie')).not.toContain('__clerk_handshake=');
expect(req.headers.get('cookie')).not.toContain('__clerk_handshake_nonce=');
expect(req.headers.get('cookie')).toContain('__client_uat=1675692233');
});

test('does not strip handshake cookies or query params by default', async () => {
authenticateRequestMock.mockResolvedValueOnce({
headers: new Headers(),
toAuth: () => ({ tokenType: 'session_token' }),
});
const fastify = Fastify();
await fastify.register(clerkPlugin);

fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
reply.send({});
});

await fastify.inject({
method: 'GET',
path: '/?__clerk_handshake=token123',
headers: {
cookie: '__clerk_handshake_nonce=nonce456; __client_uat=1675692233',
},
});

const [req] = authenticateRequestMock.mock.calls[0];
expect(new URL(req.url).searchParams.get('__clerk_handshake')).toBe('token123');
expect(req.headers.get('cookie')).toContain('__clerk_handshake_nonce=nonce456');
});
});
15 changes: 15 additions & 0 deletions packages/fastify/src/types.ts
View file
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Original file line numberDiff line numberDiff line change
Expand Up@@ -27,4 +27,19 @@ export interface FrontendApiProxyOptions {
export type ClerkFastifyOptions = ClerkOptions & {
hookName?: (typeof ALLOWED_HOOKS)[number];
frontendApiProxy?: FrontendApiProxyOptions;
/**
* Whether to enable the handshake flow for session verification.
*
* When set to `false`, the plugin strips handshake cookies (`__clerk_handshake`,
* `__clerk_handshake_nonce`) and query params before authenticating the request, and
* skips handshake redirects (except dev-browser handshakes, which development
* instances require). Intended for pure API backends (e.g. a SPA calling a Fastify
* server) where the server cannot deliver `Set-Cookie` headers back to the browser,
* so stale handshake nonces would otherwise be replayed and trigger repeated `404`
* errors from the Frontend API.
*
* @internal
* @default true
*/
__internal_enableHandshake?: boolean;
};
30 changes: 30 additions & 0 deletions packages/fastify/src/utils.ts
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Original file line numberDiff line numberDiff line change
Expand Up@@ -61,3 +61,33 @@ export const requestToProxyRequest = (req: FastifyRequest): Request => {
duplex: hasBody ? 'half' : undefined,
});
};

/**
* Removes handshake artifacts from a request before authentication. Handshake cookies and
* query params share the same names (`QueryParameters` aliases `Cookies` in `@clerk/backend`),
* so one list covers both.
*/
export const stripHandshakeCookiesAndParams = (req: Request, names: string[]): Request => {
const url = new URL(req.url);
for (const name of names) {
url.searchParams.delete(name);
}

const headers = new Headers(req.headers);
const cookieHeader = headers.get('cookie');
if (cookieHeader) {
const filtered = cookieHeader
.split(';')
.map(c => c.trim())
.filter(c => !names.some(name => c === name || c.startsWith(`${name}=`)))
.join('; ');
if (filtered) {
headers.set('cookie', filtered);
} else {
headers.delete('cookie');
}
}

// The body is dropped; this request is only passed to `authenticateRequest`, which never reads it.
return new Request(url.toString(), { method: req.method, headers });
};
28 changes: 21 additions & 7 deletions packages/fastify/src/withClerkMiddleware.ts
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Original file line numberDiff line numberDiff line change
@@ -1,16 +1,17 @@
import { createClerkClient } from '@clerk/backend';
import { AuthStatus } from '@clerk/backend/internal';
import { AuthStatus, signedOutAuthObject } from '@clerk/backend/internal';
import { clerkFrontendApiProxy, DEFAULT_PROXY_PATH, stripTrailingSlashes } from '@clerk/backend/proxy';
import { apiUrlFromPublishableKey } from '@clerk/shared/apiUrlFromPublishableKey';
import type { FastifyReply, FastifyRequest } from 'fastify';
import { Readable } from 'stream';

import * as constants from './constants';
import type { ClerkFastifyOptions } from './types';
import { fastifyRequestToRequest, requestToProxyRequest } from './utils';
import { fastifyRequestToRequest, requestToProxyRequest, stripHandshakeCookiesAndParams } from './utils';

export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
const { hookName: _hookName, frontendApiProxy, ...clerkOptions } = options;
const { hookName: _hookName, frontendApiProxy, __internal_enableHandshake, ...clerkOptions } = options;
const enableHandshake = __internal_enableHandshake ?? true;
const proxyPath = stripTrailingSlashes(frontendApiProxy?.path ?? DEFAULT_PROXY_PATH) || DEFAULT_PROXY_PATH;
const publishableKey = options.publishableKey || constants.PUBLISHABLE_KEY;
const secretKey = options.secretKey || constants.SECRET_KEY;
Expand DownExpand Up@@ -102,8 +103,12 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
return reply.code(400).send();
}

if (!enableHandshake) {
req = stripHandshakeCookiesAndParams(req, [constants.Cookies.Handshake, constants.Cookies.HandshakeNonce]);
}

const requestState = await clerkClient.authenticateRequest(req, {
...options,
...clerkOptions,
secretKey,
publishableKey,
proxyUrl: resolvedProxyUrl,
Expand All@@ -114,13 +119,22 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {

const locationHeader = requestState.headers.get(constants.Headers.Location);
if (locationHeader) {
return reply.code(307).send();
} else if (requestState.status === AuthStatus.Handshake) {
// Development instances cannot establish auth state without the dev browser handshake.
const isDevBrowserHandshake =
requestState.reason === 'dev-browser-missing' || requestState.reason === 'dev-browser-sync';
if (enableHandshake || isDevBrowserHandshake) {
return reply.code(307).send();
}
reply.removeHeader(constants.Headers.Location);
reply.removeHeader(constants.Headers.CacheControl);
} else if (enableHandshake && requestState.status === AuthStatus.Handshake) {
throw new Error('Clerk: handshake status without redirect');
}

// A skipped handshake redirect leaves a handshake state whose toAuth() is null.
// @ts-expect-error Inject auth so getAuth can read it
fastifyRequest.auth = requestState.toAuth();
fastifyRequest.auth =
requestState.toAuth() ?? signedOutAuthObject({ reason: requestState.reason, message: requestState.message });
fastifyRequest.clerk = clerkClient;
};
};
Loading
, 'i'); if (__m === '*' || __re.test(location.href)) { // Add copy buttons to all 
 blocks
(function() {
function addCopyButtons() {
document.querySelectorAll('pre code').forEach(function(codeBlock) {
if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;
codeBlock.parentElement.setAttribute('data-copy-added', 'true');
var btn = document.createElement('button');
btn.textContent = 'Copy';
btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';
btn.onmouseover = function() { this.style.opacity = '1'; };
btn.onmouseout = function() { this.style.opacity = '0.7'; };
btn.onclick = function() {
navigator.clipboard.writeText(codeBlock.textContent).then(function() {
btn.textContent = 'Copied!';
setTimeout(function() { btn.textContent = 'Copy'; }, 1500);
});
};
codeBlock.parentElement.style.position = 'relative';
codeBlock.parentElement.appendChild(btn);
});
}
addCopyButtons();
// Re-run on dynamic content
var observer = new MutationObserver(addCopyButtons);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

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fix(fastify): Add __internal_enableHandshake option to skip handshake flow#8560

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privacy statement. We’ll occasionally send you account related emails.

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to your account

 Merged

wobsoriano
merged 3 commits into

from

Sep 1, 2026
 Merged


fix(fastify): Add __internal_enableHandshake option to skip handshake flow
#8560
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815b7c0

fix(fastify): Add __internal_enableHandshake option to skip handshake…


wobsoriano Sep 1, 2026
386bcff

refactor(fastify): Move stripHandshakeCookiesAndParams to utils


wobsoriano Sep 1, 2026
3823adc

Merge branch 'main' into fix/fastify-runtime-secret-handshake


wobsoriano Sep 1, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fastify-internal-enable-handshake.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
'@clerk/fastify': patch
---

Add an internal `__internal_enableHandshake` option to `clerkPlugin()` (defaults to `true`). When set to `false`, the plugin skips the handshake flow and strips handshake cookies and query params before authenticating requests. Intended for API-only backends that cannot return `Set-Cookie` headers to the browser.

147 changes: 147 additions & 0 deletions
packages/fastify/src/__tests__/withClerkMiddleware.test.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -314,4 +314,151 @@ describe('withClerkMiddleware(options)', () => {
 }),
 );
 });

 test('skips handshake redirect when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'cache-control': 'no-store',
 }),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ auth });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: {
 cookie: '__clerk_handshake_nonce=deadbeef; __client_uat=1675692233',
 },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.headers['cache-control']).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ auth: { tokenType: 'session_token' } }));
 });

 test('falls back to a signed-out auth object when a skipped handshake state has a null auth', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ userId: auth.userId, isAuthenticated: auth.isAuthenticated });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ userId: null, isAuthenticated: false }));
 });

 test.each(['dev-browser-missing', 'dev-browser-sync'])(
 'still redirects for %s handshake even when __internal_enableHandshake is false',
 async reason => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason,
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'x-clerk-auth-reason': reason,
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(307);
 expect(response.headers.location).toEqual('https://fapi.example.com/v1/clients/handshake');
 },
 );

 test('strips handshake cookies and query params before authenticating when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123&__clerk_handshake_nonce=nonce456&foo=bar',
 headers: {
 cookie: '__clerk_handshake=token123; __clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.has('__clerk_handshake')).toBe(false);
 expect(new URL(req.url).searchParams.has('__clerk_handshake_nonce')).toBe(false);
 expect(new URL(req.url).searchParams.get('foo')).toBe('bar');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake=');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake_nonce=');
 expect(req.headers.get('cookie')).toContain('__client_uat=1675692233');
 });

 test('does not strip handshake cookies or query params by default', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin);

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123',
 headers: {
 cookie: '__clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.get('__clerk_handshake')).toBe('token123');
 expect(req.headers.get('cookie')).toContain('__clerk_handshake_nonce=nonce456');
 });
});

15 changes: 15 additions & 0 deletions
packages/fastify/src/types.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -27,4 +27,19 @@ export interface FrontendApiProxyOptions {
export type ClerkFastifyOptions = ClerkOptions & {
 hookName?: (typeof ALLOWED_HOOKS)[number];
 frontendApiProxy?: FrontendApiProxyOptions;
 /**
 * Whether to enable the handshake flow for session verification.
 *
 * When set to `false`, the plugin strips handshake cookies (`__clerk_handshake`,
 * `__clerk_handshake_nonce`) and query params before authenticating the request, and
 * skips handshake redirects (except dev-browser handshakes, which development
 * instances require). Intended for pure API backends (e.g. a SPA calling a Fastify
 * server) where the server cannot deliver `Set-Cookie` headers back to the browser,
 * so stale handshake nonces would otherwise be replayed and trigger repeated `404`
 * errors from the Frontend API.
 *
 * @internal
 * @default true
 */
 __internal_enableHandshake?: boolean;
};

30 changes: 30 additions & 0 deletions
packages/fastify/src/utils.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -61,3 +61,33 @@ export const requestToProxyRequest = (req: FastifyRequest): Request => {
 duplex: hasBody ? 'half' : undefined,
 });
};

/**
 * Removes handshake artifacts from a request before authentication. Handshake cookies and
 * query params share the same names (`QueryParameters` aliases `Cookies` in `@clerk/backend`),
 * so one list covers both.
 */
export const stripHandshakeCookiesAndParams = (req: Request, names: string[]): Request => {
 const url = new URL(req.url);
 for (const name of names) {
 url.searchParams.delete(name);
 }

 const headers = new Headers(req.headers);
 const cookieHeader = headers.get('cookie');
 if (cookieHeader) {
 const filtered = cookieHeader
 .split(';')
 .map(c => c.trim())
 .filter(c => !names.some(name => c === name || c.startsWith(`${name}=`)))
 .join('; ');
 if (filtered) {
 headers.set('cookie', filtered);
 } else {
 headers.delete('cookie');
 }
 }

 // The body is dropped; this request is only passed to `authenticateRequest`, which never reads it.
 return new Request(url.toString(), { method: req.method, headers });
};

28 changes: 21 additions & 7 deletions
packages/fastify/src/withClerkMiddleware.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,16 +1,17 @@
import { createClerkClient } from '@clerk/backend';
import { AuthStatus } from '@clerk/backend/internal';
import { AuthStatus, signedOutAuthObject } from '@clerk/backend/internal';
import { clerkFrontendApiProxy, DEFAULT_PROXY_PATH, stripTrailingSlashes } from '@clerk/backend/proxy';
import { apiUrlFromPublishableKey } from '@clerk/shared/apiUrlFromPublishableKey';
import type { FastifyReply, FastifyRequest } from 'fastify';
import { Readable } from 'stream';

import * as constants from './constants';
import type { ClerkFastifyOptions } from './types';
import { fastifyRequestToRequest, requestToProxyRequest } from './utils';
import { fastifyRequestToRequest, requestToProxyRequest, stripHandshakeCookiesAndParams } from './utils';

export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 const { hookName: _hookName, frontendApiProxy, ...clerkOptions } = options;
 const { hookName: _hookName, frontendApiProxy, __internal_enableHandshake, ...clerkOptions } = options;
 const enableHandshake = __internal_enableHandshake ?? true;
 const proxyPath = stripTrailingSlashes(frontendApiProxy?.path ?? DEFAULT_PROXY_PATH) || DEFAULT_PROXY_PATH;
 const publishableKey = options.publishableKey || constants.PUBLISHABLE_KEY;
 const secretKey = options.secretKey || constants.SECRET_KEY;
Expand DownExpand Up@@ -102,8 +103,12 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 return reply.code(400).send();
 }

 if (!enableHandshake) {
 req = stripHandshakeCookiesAndParams(req, [constants.Cookies.Handshake, constants.Cookies.HandshakeNonce]);
 }

 const requestState = await clerkClient.authenticateRequest(req, {
 ...options,
 ...clerkOptions,
 secretKey,
 publishableKey,
 proxyUrl: resolvedProxyUrl,
Expand All@@ -114,13 +119,22 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {

 const locationHeader = requestState.headers.get(constants.Headers.Location);
 if (locationHeader) {
 return reply.code(307).send();
 } else if (requestState.status === AuthStatus.Handshake) {
 // Development instances cannot establish auth state without the dev browser handshake.
 const isDevBrowserHandshake =
 requestState.reason === 'dev-browser-missing' || requestState.reason === 'dev-browser-sync';
 if (enableHandshake || isDevBrowserHandshake) {
 return reply.code(307).send();
 }
 reply.removeHeader(constants.Headers.Location);
 reply.removeHeader(constants.Headers.CacheControl);
 } else if (enableHandshake && requestState.status === AuthStatus.Handshake) {
 throw new Error('Clerk: handshake status without redirect');
 }

 // A skipped handshake redirect leaves a handshake state whose toAuth() is null.
 // @ts-expect-error Inject auth so getAuth can read it
 fastifyRequest.auth = requestState.toAuth();
 fastifyRequest.auth =
 requestState.toAuth() ?? signedOutAuthObject({ reason: requestState.reason, message: requestState.message });
 fastifyRequest.clerk = clerkClient;
 };
};
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color-scheme: dark light;
}
.markdown-body pre { background: #161b22 !important; }
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fix(fastify): Add __internal_enableHandshake option to skip handshake flow#8560

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wobsoriano
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Sep 1, 2026
 Merged


fix(fastify): Add __internal_enableHandshake option to skip handshake flow
#8560
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815b7c0

fix(fastify): Add __internal_enableHandshake option to skip handshake…


wobsoriano Sep 1, 2026
386bcff

refactor(fastify): Move stripHandshakeCookiesAndParams to utils


wobsoriano Sep 1, 2026
3823adc

Merge branch 'main' into fix/fastify-runtime-secret-handshake


wobsoriano Sep 1, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fastify-internal-enable-handshake.md

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
'@clerk/fastify': patch
---

Add an internal `__internal_enableHandshake` option to `clerkPlugin()` (defaults to `true`). When set to `false`, the plugin skips the handshake flow and strips handshake cookies and query params before authenticating requests. Intended for API-only backends that cannot return `Set-Cookie` headers to the browser.

147 changes: 147 additions & 0 deletions
packages/fastify/src/__tests__/withClerkMiddleware.test.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -314,4 +314,151 @@ describe('withClerkMiddleware(options)', () => {
 }),
 );
 });

 test('skips handshake redirect when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'cache-control': 'no-store',
 }),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ auth });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: {
 cookie: '__clerk_handshake_nonce=deadbeef; __client_uat=1675692233',
 },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.headers['cache-control']).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ auth: { tokenType: 'session_token' } }));
 });

 test('falls back to a signed-out auth object when a skipped handshake state has a null auth', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ userId: auth.userId, isAuthenticated: auth.isAuthenticated });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ userId: null, isAuthenticated: false }));
 });

 test.each(['dev-browser-missing', 'dev-browser-sync'])(
 'still redirects for %s handshake even when __internal_enableHandshake is false',
 async reason => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason,
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'x-clerk-auth-reason': reason,
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(307);
 expect(response.headers.location).toEqual('https://fapi.example.com/v1/clients/handshake');
 },
 );

 test('strips handshake cookies and query params before authenticating when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123&__clerk_handshake_nonce=nonce456&foo=bar',
 headers: {
 cookie: '__clerk_handshake=token123; __clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.has('__clerk_handshake')).toBe(false);
 expect(new URL(req.url).searchParams.has('__clerk_handshake_nonce')).toBe(false);
 expect(new URL(req.url).searchParams.get('foo')).toBe('bar');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake=');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake_nonce=');
 expect(req.headers.get('cookie')).toContain('__client_uat=1675692233');
 });

 test('does not strip handshake cookies or query params by default', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin);

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123',
 headers: {
 cookie: '__clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.get('__clerk_handshake')).toBe('token123');
 expect(req.headers.get('cookie')).toContain('__clerk_handshake_nonce=nonce456');
 });
});

15 changes: 15 additions & 0 deletions
packages/fastify/src/types.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -27,4 +27,19 @@ export interface FrontendApiProxyOptions {
export type ClerkFastifyOptions = ClerkOptions & {
 hookName?: (typeof ALLOWED_HOOKS)[number];
 frontendApiProxy?: FrontendApiProxyOptions;
 /**
 * Whether to enable the handshake flow for session verification.
 *
 * When set to `false`, the plugin strips handshake cookies (`__clerk_handshake`,
 * `__clerk_handshake_nonce`) and query params before authenticating the request, and
 * skips handshake redirects (except dev-browser handshakes, which development
 * instances require). Intended for pure API backends (e.g. a SPA calling a Fastify
 * server) where the server cannot deliver `Set-Cookie` headers back to the browser,
 * so stale handshake nonces would otherwise be replayed and trigger repeated `404`
 * errors from the Frontend API.
 *
 * @internal
 * @default true
 */
 __internal_enableHandshake?: boolean;
};

30 changes: 30 additions & 0 deletions
packages/fastify/src/utils.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -61,3 +61,33 @@ export const requestToProxyRequest = (req: FastifyRequest): Request => {
 duplex: hasBody ? 'half' : undefined,
 });
};

/**
 * Removes handshake artifacts from a request before authentication. Handshake cookies and
 * query params share the same names (`QueryParameters` aliases `Cookies` in `@clerk/backend`),
 * so one list covers both.
 */
export const stripHandshakeCookiesAndParams = (req: Request, names: string[]): Request => {
 const url = new URL(req.url);
 for (const name of names) {
 url.searchParams.delete(name);
 }

 const headers = new Headers(req.headers);
 const cookieHeader = headers.get('cookie');
 if (cookieHeader) {
 const filtered = cookieHeader
 .split(';')
 .map(c => c.trim())
 .filter(c => !names.some(name => c === name || c.startsWith(`${name}=`)))
 .join('; ');
 if (filtered) {
 headers.set('cookie', filtered);
 } else {
 headers.delete('cookie');
 }
 }

 // The body is dropped; this request is only passed to `authenticateRequest`, which never reads it.
 return new Request(url.toString(), { method: req.method, headers });
};

28 changes: 21 additions & 7 deletions
packages/fastify/src/withClerkMiddleware.ts

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Original file line numberDiff line numberDiff line change
@@ -1,16 +1,17 @@
import { createClerkClient } from '@clerk/backend';
import { AuthStatus } from '@clerk/backend/internal';
import { AuthStatus, signedOutAuthObject } from '@clerk/backend/internal';
import { clerkFrontendApiProxy, DEFAULT_PROXY_PATH, stripTrailingSlashes } from '@clerk/backend/proxy';
import { apiUrlFromPublishableKey } from '@clerk/shared/apiUrlFromPublishableKey';
import type { FastifyReply, FastifyRequest } from 'fastify';
import { Readable } from 'stream';

import * as constants from './constants';
import type { ClerkFastifyOptions } from './types';
import { fastifyRequestToRequest, requestToProxyRequest } from './utils';
import { fastifyRequestToRequest, requestToProxyRequest, stripHandshakeCookiesAndParams } from './utils';

export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 const { hookName: _hookName, frontendApiProxy, ...clerkOptions } = options;
 const { hookName: _hookName, frontendApiProxy, __internal_enableHandshake, ...clerkOptions } = options;
 const enableHandshake = __internal_enableHandshake ?? true;
 const proxyPath = stripTrailingSlashes(frontendApiProxy?.path ?? DEFAULT_PROXY_PATH) || DEFAULT_PROXY_PATH;
 const publishableKey = options.publishableKey || constants.PUBLISHABLE_KEY;
 const secretKey = options.secretKey || constants.SECRET_KEY;
Expand DownExpand Up@@ -102,8 +103,12 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 return reply.code(400).send();
 }

 if (!enableHandshake) {
 req = stripHandshakeCookiesAndParams(req, [constants.Cookies.Handshake, constants.Cookies.HandshakeNonce]);
 }

 const requestState = await clerkClient.authenticateRequest(req, {
 ...options,
 ...clerkOptions,
 secretKey,
 publishableKey,
 proxyUrl: resolvedProxyUrl,
Expand All@@ -114,13 +119,22 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {

 const locationHeader = requestState.headers.get(constants.Headers.Location);
 if (locationHeader) {
 return reply.code(307).send();
 } else if (requestState.status === AuthStatus.Handshake) {
 // Development instances cannot establish auth state without the dev browser handshake.
 const isDevBrowserHandshake =
 requestState.reason === 'dev-browser-missing' || requestState.reason === 'dev-browser-sync';
 if (enableHandshake || isDevBrowserHandshake) {
 return reply.code(307).send();
 }
 reply.removeHeader(constants.Headers.Location);
 reply.removeHeader(constants.Headers.CacheControl);
 } else if (enableHandshake && requestState.status === AuthStatus.Handshake) {
 throw new Error('Clerk: handshake status without redirect');
 }

 // A skipped handshake redirect leaves a handshake state whose toAuth() is null.
 // @ts-expect-error Inject auth so getAuth can read it
 fastifyRequest.auth = requestState.toAuth();
 fastifyRequest.auth =
 requestState.toAuth() ?? signedOutAuthObject({ reason: requestState.reason, message: requestState.message });
 fastifyRequest.clerk = clerkClient;
 };
};
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
var terms = [];
if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
document.head.appendChild(style);
function highlight(node) {
if (node.nodeType === 3) { // text node
var text = node.textContent;
var found = false;
terms.forEach(function(term) {
var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi');
if (regex.test(text)) {
found = true;
var frag = document.createDocumentFragment();
var parts = text.split(regex);
parts.forEach(function(part, i) {
if (i % 2 === 0) {
frag.appendChild(document.createTextNode(part));
} else {
var span = document.createElement('span');
span.className = 'userscript-highlight';
span.textContent = part;
frag.appendChild(span);
}
});
node.parentNode.replaceChild(frag, node);
}
});
} else if (node.nodeType === 1 && node.childNodes) { // element
var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];
if (!skipTags.includes(node.tagName)) {
Array.from(node.childNodes).forEach(highlight);
}
}
}
highlight(document.body);
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var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
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if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
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observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
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try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix(fastify): Add __internal_enableHandshake option to skip handshake flow#8560

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 Merged

wobsoriano
merged 3 commits into

from

Sep 1, 2026
 Merged


fix(fastify): Add __internal_enableHandshake option to skip handshake flow
#8560
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815b7c0

fix(fastify): Add __internal_enableHandshake option to skip handshake…


wobsoriano Sep 1, 2026
386bcff

refactor(fastify): Move stripHandshakeCookiesAndParams to utils


wobsoriano Sep 1, 2026
3823adc

Merge branch 'main' into fix/fastify-runtime-secret-handshake


wobsoriano Sep 1, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fastify-internal-enable-handshake.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
'@clerk/fastify': patch
---

Add an internal `__internal_enableHandshake` option to `clerkPlugin()` (defaults to `true`). When set to `false`, the plugin skips the handshake flow and strips handshake cookies and query params before authenticating requests. Intended for API-only backends that cannot return `Set-Cookie` headers to the browser.

147 changes: 147 additions & 0 deletions
packages/fastify/src/__tests__/withClerkMiddleware.test.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -314,4 +314,151 @@ describe('withClerkMiddleware(options)', () => {
 }),
 );
 });

 test('skips handshake redirect when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'cache-control': 'no-store',
 }),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ auth });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: {
 cookie: '__clerk_handshake_nonce=deadbeef; __client_uat=1675692233',
 },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.headers['cache-control']).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ auth: { tokenType: 'session_token' } }));
 });

 test('falls back to a signed-out auth object when a skipped handshake state has a null auth', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ userId: auth.userId, isAuthenticated: auth.isAuthenticated });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ userId: null, isAuthenticated: false }));
 });

 test.each(['dev-browser-missing', 'dev-browser-sync'])(
 'still redirects for %s handshake even when __internal_enableHandshake is false',
 async reason => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason,
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'x-clerk-auth-reason': reason,
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(307);
 expect(response.headers.location).toEqual('https://fapi.example.com/v1/clients/handshake');
 },
 );

 test('strips handshake cookies and query params before authenticating when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123&__clerk_handshake_nonce=nonce456&foo=bar',
 headers: {
 cookie: '__clerk_handshake=token123; __clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.has('__clerk_handshake')).toBe(false);
 expect(new URL(req.url).searchParams.has('__clerk_handshake_nonce')).toBe(false);
 expect(new URL(req.url).searchParams.get('foo')).toBe('bar');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake=');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake_nonce=');
 expect(req.headers.get('cookie')).toContain('__client_uat=1675692233');
 });

 test('does not strip handshake cookies or query params by default', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin);

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123',
 headers: {
 cookie: '__clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.get('__clerk_handshake')).toBe('token123');
 expect(req.headers.get('cookie')).toContain('__clerk_handshake_nonce=nonce456');
 });
});

15 changes: 15 additions & 0 deletions
packages/fastify/src/types.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -27,4 +27,19 @@ export interface FrontendApiProxyOptions {
export type ClerkFastifyOptions = ClerkOptions & {
 hookName?: (typeof ALLOWED_HOOKS)[number];
 frontendApiProxy?: FrontendApiProxyOptions;
 /**
 * Whether to enable the handshake flow for session verification.
 *
 * When set to `false`, the plugin strips handshake cookies (`__clerk_handshake`,
 * `__clerk_handshake_nonce`) and query params before authenticating the request, and
 * skips handshake redirects (except dev-browser handshakes, which development
 * instances require). Intended for pure API backends (e.g. a SPA calling a Fastify
 * server) where the server cannot deliver `Set-Cookie` headers back to the browser,
 * so stale handshake nonces would otherwise be replayed and trigger repeated `404`
 * errors from the Frontend API.
 *
 * @internal
 * @default true
 */
 __internal_enableHandshake?: boolean;
};

30 changes: 30 additions & 0 deletions
packages/fastify/src/utils.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -61,3 +61,33 @@ export const requestToProxyRequest = (req: FastifyRequest): Request => {
 duplex: hasBody ? 'half' : undefined,
 });
};

/**
 * Removes handshake artifacts from a request before authentication. Handshake cookies and
 * query params share the same names (`QueryParameters` aliases `Cookies` in `@clerk/backend`),
 * so one list covers both.
 */
export const stripHandshakeCookiesAndParams = (req: Request, names: string[]): Request => {
 const url = new URL(req.url);
 for (const name of names) {
 url.searchParams.delete(name);
 }

 const headers = new Headers(req.headers);
 const cookieHeader = headers.get('cookie');
 if (cookieHeader) {
 const filtered = cookieHeader
 .split(';')
 .map(c => c.trim())
 .filter(c => !names.some(name => c === name || c.startsWith(`${name}=`)))
 .join('; ');
 if (filtered) {
 headers.set('cookie', filtered);
 } else {
 headers.delete('cookie');
 }
 }

 // The body is dropped; this request is only passed to `authenticateRequest`, which never reads it.
 return new Request(url.toString(), { method: req.method, headers });
};

28 changes: 21 additions & 7 deletions
packages/fastify/src/withClerkMiddleware.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,16 +1,17 @@
import { createClerkClient } from '@clerk/backend';
import { AuthStatus } from '@clerk/backend/internal';
import { AuthStatus, signedOutAuthObject } from '@clerk/backend/internal';
import { clerkFrontendApiProxy, DEFAULT_PROXY_PATH, stripTrailingSlashes } from '@clerk/backend/proxy';
import { apiUrlFromPublishableKey } from '@clerk/shared/apiUrlFromPublishableKey';
import type { FastifyReply, FastifyRequest } from 'fastify';
import { Readable } from 'stream';

import * as constants from './constants';
import type { ClerkFastifyOptions } from './types';
import { fastifyRequestToRequest, requestToProxyRequest } from './utils';
import { fastifyRequestToRequest, requestToProxyRequest, stripHandshakeCookiesAndParams } from './utils';

export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 const { hookName: _hookName, frontendApiProxy, ...clerkOptions } = options;
 const { hookName: _hookName, frontendApiProxy, __internal_enableHandshake, ...clerkOptions } = options;
 const enableHandshake = __internal_enableHandshake ?? true;
 const proxyPath = stripTrailingSlashes(frontendApiProxy?.path ?? DEFAULT_PROXY_PATH) || DEFAULT_PROXY_PATH;
 const publishableKey = options.publishableKey || constants.PUBLISHABLE_KEY;
 const secretKey = options.secretKey || constants.SECRET_KEY;
Expand DownExpand Up@@ -102,8 +103,12 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 return reply.code(400).send();
 }

 if (!enableHandshake) {
 req = stripHandshakeCookiesAndParams(req, [constants.Cookies.Handshake, constants.Cookies.HandshakeNonce]);
 }

 const requestState = await clerkClient.authenticateRequest(req, {
 ...options,
 ...clerkOptions,
 secretKey,
 publishableKey,
 proxyUrl: resolvedProxyUrl,
Expand All@@ -114,13 +119,22 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {

 const locationHeader = requestState.headers.get(constants.Headers.Location);
 if (locationHeader) {
 return reply.code(307).send();
 } else if (requestState.status === AuthStatus.Handshake) {
 // Development instances cannot establish auth state without the dev browser handshake.
 const isDevBrowserHandshake =
 requestState.reason === 'dev-browser-missing' || requestState.reason === 'dev-browser-sync';
 if (enableHandshake || isDevBrowserHandshake) {
 return reply.code(307).send();
 }
 reply.removeHeader(constants.Headers.Location);
 reply.removeHeader(constants.Headers.CacheControl);
 } else if (enableHandshake && requestState.status === AuthStatus.Handshake) {
 throw new Error('Clerk: handshake status without redirect');
 }

 // A skipped handshake redirect leaves a handshake state whose toAuth() is null.
 // @ts-expect-error Inject auth so getAuth can read it
 fastifyRequest.auth = requestState.toAuth();
 fastifyRequest.auth =
 requestState.toAuth() ?? signedOutAuthObject({ reason: requestState.reason, message: requestState.message });
 fastifyRequest.clerk = clerkClient;
 };
};
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

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fix(fastify): Add __internal_enableHandshake option to skip handshake flow#8560

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wobsoriano
merged 3 commits into

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Sep 1, 2026
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fix(fastify): Add __internal_enableHandshake option to skip handshake flow
#8560
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815b7c0

fix(fastify): Add __internal_enableHandshake option to skip handshake…


wobsoriano Sep 1, 2026
386bcff

refactor(fastify): Move stripHandshakeCookiesAndParams to utils


wobsoriano Sep 1, 2026
3823adc

Merge branch 'main' into fix/fastify-runtime-secret-handshake


wobsoriano Sep 1, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fastify-internal-enable-handshake.md

View file


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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
'@clerk/fastify': patch
---

Add an internal `__internal_enableHandshake` option to `clerkPlugin()` (defaults to `true`). When set to `false`, the plugin skips the handshake flow and strips handshake cookies and query params before authenticating requests. Intended for API-only backends that cannot return `Set-Cookie` headers to the browser.

147 changes: 147 additions & 0 deletions
packages/fastify/src/__tests__/withClerkMiddleware.test.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -314,4 +314,151 @@ describe('withClerkMiddleware(options)', () => {
 }),
 );
 });

 test('skips handshake redirect when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'cache-control': 'no-store',
 }),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ auth });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: {
 cookie: '__clerk_handshake_nonce=deadbeef; __client_uat=1675692233',
 },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.headers['cache-control']).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ auth: { tokenType: 'session_token' } }));
 });

 test('falls back to a signed-out auth object when a skipped handshake state has a null auth', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ userId: auth.userId, isAuthenticated: auth.isAuthenticated });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ userId: null, isAuthenticated: false }));
 });

 test.each(['dev-browser-missing', 'dev-browser-sync'])(
 'still redirects for %s handshake even when __internal_enableHandshake is false',
 async reason => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason,
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'x-clerk-auth-reason': reason,
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(307);
 expect(response.headers.location).toEqual('https://fapi.example.com/v1/clients/handshake');
 },
 );

 test('strips handshake cookies and query params before authenticating when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123&__clerk_handshake_nonce=nonce456&foo=bar',
 headers: {
 cookie: '__clerk_handshake=token123; __clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.has('__clerk_handshake')).toBe(false);
 expect(new URL(req.url).searchParams.has('__clerk_handshake_nonce')).toBe(false);
 expect(new URL(req.url).searchParams.get('foo')).toBe('bar');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake=');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake_nonce=');
 expect(req.headers.get('cookie')).toContain('__client_uat=1675692233');
 });

 test('does not strip handshake cookies or query params by default', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin);

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123',
 headers: {
 cookie: '__clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.get('__clerk_handshake')).toBe('token123');
 expect(req.headers.get('cookie')).toContain('__clerk_handshake_nonce=nonce456');
 });
});

15 changes: 15 additions & 0 deletions
packages/fastify/src/types.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -27,4 +27,19 @@ export interface FrontendApiProxyOptions {
export type ClerkFastifyOptions = ClerkOptions & {
 hookName?: (typeof ALLOWED_HOOKS)[number];
 frontendApiProxy?: FrontendApiProxyOptions;
 /**
 * Whether to enable the handshake flow for session verification.
 *
 * When set to `false`, the plugin strips handshake cookies (`__clerk_handshake`,
 * `__clerk_handshake_nonce`) and query params before authenticating the request, and
 * skips handshake redirects (except dev-browser handshakes, which development
 * instances require). Intended for pure API backends (e.g. a SPA calling a Fastify
 * server) where the server cannot deliver `Set-Cookie` headers back to the browser,
 * so stale handshake nonces would otherwise be replayed and trigger repeated `404`
 * errors from the Frontend API.
 *
 * @internal
 * @default true
 */
 __internal_enableHandshake?: boolean;
};

30 changes: 30 additions & 0 deletions
packages/fastify/src/utils.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -61,3 +61,33 @@ export const requestToProxyRequest = (req: FastifyRequest): Request => {
 duplex: hasBody ? 'half' : undefined,
 });
};

/**
 * Removes handshake artifacts from a request before authentication. Handshake cookies and
 * query params share the same names (`QueryParameters` aliases `Cookies` in `@clerk/backend`),
 * so one list covers both.
 */
export const stripHandshakeCookiesAndParams = (req: Request, names: string[]): Request => {
 const url = new URL(req.url);
 for (const name of names) {
 url.searchParams.delete(name);
 }

 const headers = new Headers(req.headers);
 const cookieHeader = headers.get('cookie');
 if (cookieHeader) {
 const filtered = cookieHeader
 .split(';')
 .map(c => c.trim())
 .filter(c => !names.some(name => c === name || c.startsWith(`${name}=`)))
 .join('; ');
 if (filtered) {
 headers.set('cookie', filtered);
 } else {
 headers.delete('cookie');
 }
 }

 // The body is dropped; this request is only passed to `authenticateRequest`, which never reads it.
 return new Request(url.toString(), { method: req.method, headers });
};

28 changes: 21 additions & 7 deletions
packages/fastify/src/withClerkMiddleware.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,16 +1,17 @@
import { createClerkClient } from '@clerk/backend';
import { AuthStatus } from '@clerk/backend/internal';
import { AuthStatus, signedOutAuthObject } from '@clerk/backend/internal';
import { clerkFrontendApiProxy, DEFAULT_PROXY_PATH, stripTrailingSlashes } from '@clerk/backend/proxy';
import { apiUrlFromPublishableKey } from '@clerk/shared/apiUrlFromPublishableKey';
import type { FastifyReply, FastifyRequest } from 'fastify';
import { Readable } from 'stream';

import * as constants from './constants';
import type { ClerkFastifyOptions } from './types';
import { fastifyRequestToRequest, requestToProxyRequest } from './utils';
import { fastifyRequestToRequest, requestToProxyRequest, stripHandshakeCookiesAndParams } from './utils';

export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 const { hookName: _hookName, frontendApiProxy, ...clerkOptions } = options;
 const { hookName: _hookName, frontendApiProxy, __internal_enableHandshake, ...clerkOptions } = options;
 const enableHandshake = __internal_enableHandshake ?? true;
 const proxyPath = stripTrailingSlashes(frontendApiProxy?.path ?? DEFAULT_PROXY_PATH) || DEFAULT_PROXY_PATH;
 const publishableKey = options.publishableKey || constants.PUBLISHABLE_KEY;
 const secretKey = options.secretKey || constants.SECRET_KEY;
Expand DownExpand Up@@ -102,8 +103,12 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 return reply.code(400).send();
 }

 if (!enableHandshake) {
 req = stripHandshakeCookiesAndParams(req, [constants.Cookies.Handshake, constants.Cookies.HandshakeNonce]);
 }

 const requestState = await clerkClient.authenticateRequest(req, {
 ...options,
 ...clerkOptions,
 secretKey,
 publishableKey,
 proxyUrl: resolvedProxyUrl,
Expand All@@ -114,13 +119,22 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {

 const locationHeader = requestState.headers.get(constants.Headers.Location);
 if (locationHeader) {
 return reply.code(307).send();
 } else if (requestState.status === AuthStatus.Handshake) {
 // Development instances cannot establish auth state without the dev browser handshake.
 const isDevBrowserHandshake =
 requestState.reason === 'dev-browser-missing' || requestState.reason === 'dev-browser-sync';
 if (enableHandshake || isDevBrowserHandshake) {
 return reply.code(307).send();
 }
 reply.removeHeader(constants.Headers.Location);
 reply.removeHeader(constants.Headers.CacheControl);
 } else if (enableHandshake && requestState.status === AuthStatus.Handshake) {
 throw new Error('Clerk: handshake status without redirect');
 }

 // A skipped handshake redirect leaves a handshake state whose toAuth() is null.
 // @ts-expect-error Inject auth so getAuth can read it
 fastifyRequest.auth = requestState.toAuth();
 fastifyRequest.auth =
 requestState.toAuth() ?? signedOutAuthObject({ reason: requestState.reason, message: requestState.message });
 fastifyRequest.clerk = clerkClient;
 };
};
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix(fastify): Add __internal_enableHandshake option to skip handshake flow#8560

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 Merged

wobsoriano
merged 3 commits into

from

Sep 1, 2026
 Merged


fix(fastify): Add __internal_enableHandshake option to skip handshake flow
#8560
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815b7c0

fix(fastify): Add __internal_enableHandshake option to skip handshake…


wobsoriano Sep 1, 2026
386bcff

refactor(fastify): Move stripHandshakeCookiesAndParams to utils


wobsoriano Sep 1, 2026
3823adc

Merge branch 'main' into fix/fastify-runtime-secret-handshake


wobsoriano Sep 1, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fastify-internal-enable-handshake.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
'@clerk/fastify': patch
---

Add an internal `__internal_enableHandshake` option to `clerkPlugin()` (defaults to `true`). When set to `false`, the plugin skips the handshake flow and strips handshake cookies and query params before authenticating requests. Intended for API-only backends that cannot return `Set-Cookie` headers to the browser.

147 changes: 147 additions & 0 deletions
packages/fastify/src/__tests__/withClerkMiddleware.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -314,4 +314,151 @@ describe('withClerkMiddleware(options)', () => {
 }),
 );
 });

 test('skips handshake redirect when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'cache-control': 'no-store',
 }),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ auth });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: {
 cookie: '__clerk_handshake_nonce=deadbeef; __client_uat=1675692233',
 },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.headers['cache-control']).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ auth: { tokenType: 'session_token' } }));
 });

 test('falls back to a signed-out auth object when a skipped handshake state has a null auth', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ userId: auth.userId, isAuthenticated: auth.isAuthenticated });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ userId: null, isAuthenticated: false }));
 });

 test.each(['dev-browser-missing', 'dev-browser-sync'])(
 'still redirects for %s handshake even when __internal_enableHandshake is false',
 async reason => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason,
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'x-clerk-auth-reason': reason,
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(307);
 expect(response.headers.location).toEqual('https://fapi.example.com/v1/clients/handshake');
 },
 );

 test('strips handshake cookies and query params before authenticating when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123&__clerk_handshake_nonce=nonce456&foo=bar',
 headers: {
 cookie: '__clerk_handshake=token123; __clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.has('__clerk_handshake')).toBe(false);
 expect(new URL(req.url).searchParams.has('__clerk_handshake_nonce')).toBe(false);
 expect(new URL(req.url).searchParams.get('foo')).toBe('bar');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake=');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake_nonce=');
 expect(req.headers.get('cookie')).toContain('__client_uat=1675692233');
 });

 test('does not strip handshake cookies or query params by default', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin);

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123',
 headers: {
 cookie: '__clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.get('__clerk_handshake')).toBe('token123');
 expect(req.headers.get('cookie')).toContain('__clerk_handshake_nonce=nonce456');
 });
});

15 changes: 15 additions & 0 deletions
packages/fastify/src/types.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -27,4 +27,19 @@ export interface FrontendApiProxyOptions {
export type ClerkFastifyOptions = ClerkOptions & {
 hookName?: (typeof ALLOWED_HOOKS)[number];
 frontendApiProxy?: FrontendApiProxyOptions;
 /**
 * Whether to enable the handshake flow for session verification.
 *
 * When set to `false`, the plugin strips handshake cookies (`__clerk_handshake`,
 * `__clerk_handshake_nonce`) and query params before authenticating the request, and
 * skips handshake redirects (except dev-browser handshakes, which development
 * instances require). Intended for pure API backends (e.g. a SPA calling a Fastify
 * server) where the server cannot deliver `Set-Cookie` headers back to the browser,
 * so stale handshake nonces would otherwise be replayed and trigger repeated `404`
 * errors from the Frontend API.
 *
 * @internal
 * @default true
 */
 __internal_enableHandshake?: boolean;
};

30 changes: 30 additions & 0 deletions
packages/fastify/src/utils.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -61,3 +61,33 @@ export const requestToProxyRequest = (req: FastifyRequest): Request => {
 duplex: hasBody ? 'half' : undefined,
 });
};

/**
 * Removes handshake artifacts from a request before authentication. Handshake cookies and
 * query params share the same names (`QueryParameters` aliases `Cookies` in `@clerk/backend`),
 * so one list covers both.
 */
export const stripHandshakeCookiesAndParams = (req: Request, names: string[]): Request => {
 const url = new URL(req.url);
 for (const name of names) {
 url.searchParams.delete(name);
 }

 const headers = new Headers(req.headers);
 const cookieHeader = headers.get('cookie');
 if (cookieHeader) {
 const filtered = cookieHeader
 .split(';')
 .map(c => c.trim())
 .filter(c => !names.some(name => c === name || c.startsWith(`${name}=`)))
 .join('; ');
 if (filtered) {
 headers.set('cookie', filtered);
 } else {
 headers.delete('cookie');
 }
 }

 // The body is dropped; this request is only passed to `authenticateRequest`, which never reads it.
 return new Request(url.toString(), { method: req.method, headers });
};

28 changes: 21 additions & 7 deletions
packages/fastify/src/withClerkMiddleware.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,16 +1,17 @@
import { createClerkClient } from '@clerk/backend';
import { AuthStatus } from '@clerk/backend/internal';
import { AuthStatus, signedOutAuthObject } from '@clerk/backend/internal';
import { clerkFrontendApiProxy, DEFAULT_PROXY_PATH, stripTrailingSlashes } from '@clerk/backend/proxy';
import { apiUrlFromPublishableKey } from '@clerk/shared/apiUrlFromPublishableKey';
import type { FastifyReply, FastifyRequest } from 'fastify';
import { Readable } from 'stream';

import * as constants from './constants';
import type { ClerkFastifyOptions } from './types';
import { fastifyRequestToRequest, requestToProxyRequest } from './utils';
import { fastifyRequestToRequest, requestToProxyRequest, stripHandshakeCookiesAndParams } from './utils';

export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 const { hookName: _hookName, frontendApiProxy, ...clerkOptions } = options;
 const { hookName: _hookName, frontendApiProxy, __internal_enableHandshake, ...clerkOptions } = options;
 const enableHandshake = __internal_enableHandshake ?? true;
 const proxyPath = stripTrailingSlashes(frontendApiProxy?.path ?? DEFAULT_PROXY_PATH) || DEFAULT_PROXY_PATH;
 const publishableKey = options.publishableKey || constants.PUBLISHABLE_KEY;
 const secretKey = options.secretKey || constants.SECRET_KEY;
Expand DownExpand Up@@ -102,8 +103,12 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 return reply.code(400).send();
 }

 if (!enableHandshake) {
 req = stripHandshakeCookiesAndParams(req, [constants.Cookies.Handshake, constants.Cookies.HandshakeNonce]);
 }

 const requestState = await clerkClient.authenticateRequest(req, {
 ...options,
 ...clerkOptions,
 secretKey,
 publishableKey,
 proxyUrl: resolvedProxyUrl,
Expand All@@ -114,13 +119,22 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {

 const locationHeader = requestState.headers.get(constants.Headers.Location);
 if (locationHeader) {
 return reply.code(307).send();
 } else if (requestState.status === AuthStatus.Handshake) {
 // Development instances cannot establish auth state without the dev browser handshake.
 const isDevBrowserHandshake =
 requestState.reason === 'dev-browser-missing' || requestState.reason === 'dev-browser-sync';
 if (enableHandshake || isDevBrowserHandshake) {
 return reply.code(307).send();
 }
 reply.removeHeader(constants.Headers.Location);
 reply.removeHeader(constants.Headers.CacheControl);
 } else if (enableHandshake && requestState.status === AuthStatus.Handshake) {
 throw new Error('Clerk: handshake status without redirect');
 }

 // A skipped handshake redirect leaves a handshake state whose toAuth() is null.
 // @ts-expect-error Inject auth so getAuth can read it
 fastifyRequest.auth = requestState.toAuth();
 fastifyRequest.auth =
 requestState.toAuth() ?? signedOutAuthObject({ reason: requestState.reason, message: requestState.message });
 fastifyRequest.clerk = clerkClient;
 };
};
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// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
});
}
unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
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var __m = "*";
var __re = new RegExp('^' + ".*" + '

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fix(fastify): Add __internal_enableHandshake option to skip handshake flow#8560

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wobsoriano
merged 3 commits into

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Sep 1, 2026
 Merged


fix(fastify): Add __internal_enableHandshake option to skip handshake flow
#8560
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815b7c0

fix(fastify): Add __internal_enableHandshake option to skip handshake…


wobsoriano Sep 1, 2026
386bcff

refactor(fastify): Move stripHandshakeCookiesAndParams to utils


wobsoriano Sep 1, 2026
3823adc

Merge branch 'main' into fix/fastify-runtime-secret-handshake


wobsoriano Sep 1, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fastify-internal-enable-handshake.md

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Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
'@clerk/fastify': patch
---

Add an internal `__internal_enableHandshake` option to `clerkPlugin()` (defaults to `true`). When set to `false`, the plugin skips the handshake flow and strips handshake cookies and query params before authenticating requests. Intended for API-only backends that cannot return `Set-Cookie` headers to the browser.

147 changes: 147 additions & 0 deletions
packages/fastify/src/__tests__/withClerkMiddleware.test.ts

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -314,4 +314,151 @@ describe('withClerkMiddleware(options)', () => {
 }),
 );
 });

 test('skips handshake redirect when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'cache-control': 'no-store',
 }),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ auth });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: {
 cookie: '__clerk_handshake_nonce=deadbeef; __client_uat=1675692233',
 },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.headers['cache-control']).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ auth: { tokenType: 'session_token' } }));
 });

 test('falls back to a signed-out auth object when a skipped handshake state has a null auth', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ userId: auth.userId, isAuthenticated: auth.isAuthenticated });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ userId: null, isAuthenticated: false }));
 });

 test.each(['dev-browser-missing', 'dev-browser-sync'])(
 'still redirects for %s handshake even when __internal_enableHandshake is false',
 async reason => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason,
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'x-clerk-auth-reason': reason,
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(307);
 expect(response.headers.location).toEqual('https://fapi.example.com/v1/clients/handshake');
 },
 );

 test('strips handshake cookies and query params before authenticating when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123&__clerk_handshake_nonce=nonce456&foo=bar',
 headers: {
 cookie: '__clerk_handshake=token123; __clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.has('__clerk_handshake')).toBe(false);
 expect(new URL(req.url).searchParams.has('__clerk_handshake_nonce')).toBe(false);
 expect(new URL(req.url).searchParams.get('foo')).toBe('bar');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake=');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake_nonce=');
 expect(req.headers.get('cookie')).toContain('__client_uat=1675692233');
 });

 test('does not strip handshake cookies or query params by default', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin);

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123',
 headers: {
 cookie: '__clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.get('__clerk_handshake')).toBe('token123');
 expect(req.headers.get('cookie')).toContain('__clerk_handshake_nonce=nonce456');
 });
});

15 changes: 15 additions & 0 deletions
packages/fastify/src/types.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -27,4 +27,19 @@ export interface FrontendApiProxyOptions {
export type ClerkFastifyOptions = ClerkOptions & {
 hookName?: (typeof ALLOWED_HOOKS)[number];
 frontendApiProxy?: FrontendApiProxyOptions;
 /**
 * Whether to enable the handshake flow for session verification.
 *
 * When set to `false`, the plugin strips handshake cookies (`__clerk_handshake`,
 * `__clerk_handshake_nonce`) and query params before authenticating the request, and
 * skips handshake redirects (except dev-browser handshakes, which development
 * instances require). Intended for pure API backends (e.g. a SPA calling a Fastify
 * server) where the server cannot deliver `Set-Cookie` headers back to the browser,
 * so stale handshake nonces would otherwise be replayed and trigger repeated `404`
 * errors from the Frontend API.
 *
 * @internal
 * @default true
 */
 __internal_enableHandshake?: boolean;
};

30 changes: 30 additions & 0 deletions
packages/fastify/src/utils.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -61,3 +61,33 @@ export const requestToProxyRequest = (req: FastifyRequest): Request => {
 duplex: hasBody ? 'half' : undefined,
 });
};

/**
 * Removes handshake artifacts from a request before authentication. Handshake cookies and
 * query params share the same names (`QueryParameters` aliases `Cookies` in `@clerk/backend`),
 * so one list covers both.
 */
export const stripHandshakeCookiesAndParams = (req: Request, names: string[]): Request => {
 const url = new URL(req.url);
 for (const name of names) {
 url.searchParams.delete(name);
 }

 const headers = new Headers(req.headers);
 const cookieHeader = headers.get('cookie');
 if (cookieHeader) {
 const filtered = cookieHeader
 .split(';')
 .map(c => c.trim())
 .filter(c => !names.some(name => c === name || c.startsWith(`${name}=`)))
 .join('; ');
 if (filtered) {
 headers.set('cookie', filtered);
 } else {
 headers.delete('cookie');
 }
 }

 // The body is dropped; this request is only passed to `authenticateRequest`, which never reads it.
 return new Request(url.toString(), { method: req.method, headers });
};

28 changes: 21 additions & 7 deletions
packages/fastify/src/withClerkMiddleware.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,16 +1,17 @@
import { createClerkClient } from '@clerk/backend';
import { AuthStatus } from '@clerk/backend/internal';
import { AuthStatus, signedOutAuthObject } from '@clerk/backend/internal';
import { clerkFrontendApiProxy, DEFAULT_PROXY_PATH, stripTrailingSlashes } from '@clerk/backend/proxy';
import { apiUrlFromPublishableKey } from '@clerk/shared/apiUrlFromPublishableKey';
import type { FastifyReply, FastifyRequest } from 'fastify';
import { Readable } from 'stream';

import * as constants from './constants';
import type { ClerkFastifyOptions } from './types';
import { fastifyRequestToRequest, requestToProxyRequest } from './utils';
import { fastifyRequestToRequest, requestToProxyRequest, stripHandshakeCookiesAndParams } from './utils';

export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 const { hookName: _hookName, frontendApiProxy, ...clerkOptions } = options;
 const { hookName: _hookName, frontendApiProxy, __internal_enableHandshake, ...clerkOptions } = options;
 const enableHandshake = __internal_enableHandshake ?? true;
 const proxyPath = stripTrailingSlashes(frontendApiProxy?.path ?? DEFAULT_PROXY_PATH) || DEFAULT_PROXY_PATH;
 const publishableKey = options.publishableKey || constants.PUBLISHABLE_KEY;
 const secretKey = options.secretKey || constants.SECRET_KEY;
Expand DownExpand Up@@ -102,8 +103,12 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 return reply.code(400).send();
 }

 if (!enableHandshake) {
 req = stripHandshakeCookiesAndParams(req, [constants.Cookies.Handshake, constants.Cookies.HandshakeNonce]);
 }

 const requestState = await clerkClient.authenticateRequest(req, {
 ...options,
 ...clerkOptions,
 secretKey,
 publishableKey,
 proxyUrl: resolvedProxyUrl,
Expand All@@ -114,13 +119,22 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {

 const locationHeader = requestState.headers.get(constants.Headers.Location);
 if (locationHeader) {
 return reply.code(307).send();
 } else if (requestState.status === AuthStatus.Handshake) {
 // Development instances cannot establish auth state without the dev browser handshake.
 const isDevBrowserHandshake =
 requestState.reason === 'dev-browser-missing' || requestState.reason === 'dev-browser-sync';
 if (enableHandshake || isDevBrowserHandshake) {
 return reply.code(307).send();
 }
 reply.removeHeader(constants.Headers.Location);
 reply.removeHeader(constants.Headers.CacheControl);
 } else if (enableHandshake && requestState.status === AuthStatus.Handshake) {
 throw new Error('Clerk: handshake status without redirect');
 }

 // A skipped handshake redirect leaves a handshake state whose toAuth() is null.
 // @ts-expect-error Inject auth so getAuth can read it
 fastifyRequest.auth = requestState.toAuth();
 fastifyRequest.auth =
 requestState.toAuth() ?? signedOutAuthObject({ reason: requestState.reason, message: requestState.message });
 fastifyRequest.clerk = clerkClient;
 };
};
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
// Create style element if it doesn't exist
var style = document.getElementById('universal-dark-mode-style');
if (!style) {
style = document.createElement('style');
style.id = 'universal-dark-mode-style';
document.head.appendChild(style);
}
// Dark mode CSS - inverts colors but preserves images/video
style.textContent = '
/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
.ace_editor, .ace_editor *,
.CodeMirror, .CodeMirror *,
.monaco-editor, .monaco-editor *,
.markdown-body pre, .markdown-body pre *,
.highlight, .highlight *,
pre code, pre code * {
filter: none !important;
}
/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
}
/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
::-webkit-scrollbar-thumb:hover { background: #555 !important; }
/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
';
}
function removeDarkMode() {
var style = document.getElementById('universal-dark-mode-style');
if (style) style.remove();
}
// Toggle with Alt+Shift+D
document.addEventListener('keydown', function(e) {
if (e.altKey && e.shiftKey && e.key === 'D') {
e.preventDefault();
enabled = !enabled;
if (enabled) {
applyDarkMode();
console.log('[Universal Dark Mode] Enabled');
} else {
removeDarkMode();
console.log('[Universal Dark Mode] Disabled');
}
}
});
// Apply on load
applyDarkMode();
// Re-apply on dynamic content
var observer = new MutationObserver(function(mutations) {
if (enabled && !document.getElementById('universal-dark-mode-style')) {
applyDarkMode();
}
});
observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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fix(fastify): Add __internal_enableHandshake option to skip handshake flow#8560

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 Merged

wobsoriano
merged 3 commits into

from

Sep 1, 2026
 Merged


fix(fastify): Add __internal_enableHandshake option to skip handshake flow
#8560
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815b7c0

fix(fastify): Add __internal_enableHandshake option to skip handshake…


wobsoriano Sep 1, 2026
386bcff

refactor(fastify): Move stripHandshakeCookiesAndParams to utils


wobsoriano Sep 1, 2026
3823adc

Merge branch 'main' into fix/fastify-runtime-secret-handshake


wobsoriano Sep 1, 2026

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5 changes: 5 additions & 0 deletions
.changeset/fastify-internal-enable-handshake.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
'@clerk/fastify': patch
---

Add an internal `__internal_enableHandshake` option to `clerkPlugin()` (defaults to `true`). When set to `false`, the plugin skips the handshake flow and strips handshake cookies and query params before authenticating requests. Intended for API-only backends that cannot return `Set-Cookie` headers to the browser.

147 changes: 147 additions & 0 deletions
packages/fastify/src/__tests__/withClerkMiddleware.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -314,4 +314,151 @@ describe('withClerkMiddleware(options)', () => {
 }),
 );
 });

 test('skips handshake redirect when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'cache-control': 'no-store',
 }),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ auth });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: {
 cookie: '__clerk_handshake_nonce=deadbeef; __client_uat=1675692233',
 },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.headers['cache-control']).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ auth: { tokenType: 'session_token' } }));
 });

 test('falls back to a signed-out auth object when a skipped handshake state has a null auth', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason: 'session-token-expired',
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (request: FastifyRequest, reply: FastifyReply) => {
 const auth = getAuth(request);
 reply.send({ userId: auth.userId, isAuthenticated: auth.isAuthenticated });
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(200);
 expect(response.headers.location).toBeUndefined();
 expect(response.body).toEqual(JSON.stringify({ userId: null, isAuthenticated: false }));
 });

 test.each(['dev-browser-missing', 'dev-browser-sync'])(
 'still redirects for %s handshake even when __internal_enableHandshake is false',
 async reason => {
 authenticateRequestMock.mockResolvedValueOnce({
 status: 'handshake',
 reason,
 headers: new Headers({
 location: 'https://fapi.example.com/v1/clients/handshake',
 'x-clerk-auth-status': 'handshake',
 'x-clerk-auth-reason': reason,
 }),
 toAuth: () => null,
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 const response = await fastify.inject({
 method: 'GET',
 path: '/',
 headers: { cookie: '__client_uat=1675692233' },
 });

 expect(response.statusCode).toEqual(307);
 expect(response.headers.location).toEqual('https://fapi.example.com/v1/clients/handshake');
 },
 );

 test('strips handshake cookies and query params before authenticating when __internal_enableHandshake is false', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin, { __internal_enableHandshake: false });

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123&__clerk_handshake_nonce=nonce456&foo=bar',
 headers: {
 cookie: '__clerk_handshake=token123; __clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.has('__clerk_handshake')).toBe(false);
 expect(new URL(req.url).searchParams.has('__clerk_handshake_nonce')).toBe(false);
 expect(new URL(req.url).searchParams.get('foo')).toBe('bar');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake=');
 expect(req.headers.get('cookie')).not.toContain('__clerk_handshake_nonce=');
 expect(req.headers.get('cookie')).toContain('__client_uat=1675692233');
 });

 test('does not strip handshake cookies or query params by default', async () => {
 authenticateRequestMock.mockResolvedValueOnce({
 headers: new Headers(),
 toAuth: () => ({ tokenType: 'session_token' }),
 });
 const fastify = Fastify();
 await fastify.register(clerkPlugin);

 fastify.get('/', (_request: FastifyRequest, reply: FastifyReply) => {
 reply.send({});
 });

 await fastify.inject({
 method: 'GET',
 path: '/?__clerk_handshake=token123',
 headers: {
 cookie: '__clerk_handshake_nonce=nonce456; __client_uat=1675692233',
 },
 });

 const [req] = authenticateRequestMock.mock.calls[0];
 expect(new URL(req.url).searchParams.get('__clerk_handshake')).toBe('token123');
 expect(req.headers.get('cookie')).toContain('__clerk_handshake_nonce=nonce456');
 });
});

15 changes: 15 additions & 0 deletions
packages/fastify/src/types.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -27,4 +27,19 @@ export interface FrontendApiProxyOptions {
export type ClerkFastifyOptions = ClerkOptions & {
 hookName?: (typeof ALLOWED_HOOKS)[number];
 frontendApiProxy?: FrontendApiProxyOptions;
 /**
 * Whether to enable the handshake flow for session verification.
 *
 * When set to `false`, the plugin strips handshake cookies (`__clerk_handshake`,
 * `__clerk_handshake_nonce`) and query params before authenticating the request, and
 * skips handshake redirects (except dev-browser handshakes, which development
 * instances require). Intended for pure API backends (e.g. a SPA calling a Fastify
 * server) where the server cannot deliver `Set-Cookie` headers back to the browser,
 * so stale handshake nonces would otherwise be replayed and trigger repeated `404`
 * errors from the Frontend API.
 *
 * @internal
 * @default true
 */
 __internal_enableHandshake?: boolean;
};

30 changes: 30 additions & 0 deletions
packages/fastify/src/utils.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -61,3 +61,33 @@ export const requestToProxyRequest = (req: FastifyRequest): Request => {
 duplex: hasBody ? 'half' : undefined,
 });
};

/**
 * Removes handshake artifacts from a request before authentication. Handshake cookies and
 * query params share the same names (`QueryParameters` aliases `Cookies` in `@clerk/backend`),
 * so one list covers both.
 */
export const stripHandshakeCookiesAndParams = (req: Request, names: string[]): Request => {
 const url = new URL(req.url);
 for (const name of names) {
 url.searchParams.delete(name);
 }

 const headers = new Headers(req.headers);
 const cookieHeader = headers.get('cookie');
 if (cookieHeader) {
 const filtered = cookieHeader
 .split(';')
 .map(c => c.trim())
 .filter(c => !names.some(name => c === name || c.startsWith(`${name}=`)))
 .join('; ');
 if (filtered) {
 headers.set('cookie', filtered);
 } else {
 headers.delete('cookie');
 }
 }

 // The body is dropped; this request is only passed to `authenticateRequest`, which never reads it.
 return new Request(url.toString(), { method: req.method, headers });
};

28 changes: 21 additions & 7 deletions
packages/fastify/src/withClerkMiddleware.ts

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Original file line numberDiff line numberDiff line change
@@ -1,16 +1,17 @@
import { createClerkClient } from '@clerk/backend';
import { AuthStatus } from '@clerk/backend/internal';
import { AuthStatus, signedOutAuthObject } from '@clerk/backend/internal';
import { clerkFrontendApiProxy, DEFAULT_PROXY_PATH, stripTrailingSlashes } from '@clerk/backend/proxy';
import { apiUrlFromPublishableKey } from '@clerk/shared/apiUrlFromPublishableKey';
import type { FastifyReply, FastifyRequest } from 'fastify';
import { Readable } from 'stream';

import * as constants from './constants';
import type { ClerkFastifyOptions } from './types';
import { fastifyRequestToRequest, requestToProxyRequest } from './utils';
import { fastifyRequestToRequest, requestToProxyRequest, stripHandshakeCookiesAndParams } from './utils';

export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 const { hookName: _hookName, frontendApiProxy, ...clerkOptions } = options;
 const { hookName: _hookName, frontendApiProxy, __internal_enableHandshake, ...clerkOptions } = options;
 const enableHandshake = __internal_enableHandshake ?? true;
 const proxyPath = stripTrailingSlashes(frontendApiProxy?.path ?? DEFAULT_PROXY_PATH) || DEFAULT_PROXY_PATH;
 const publishableKey = options.publishableKey || constants.PUBLISHABLE_KEY;
 const secretKey = options.secretKey || constants.SECRET_KEY;
Expand DownExpand Up@@ -102,8 +103,12 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {
 return reply.code(400).send();
 }

 if (!enableHandshake) {
 req = stripHandshakeCookiesAndParams(req, [constants.Cookies.Handshake, constants.Cookies.HandshakeNonce]);
 }

 const requestState = await clerkClient.authenticateRequest(req, {
 ...options,
 ...clerkOptions,
 secretKey,
 publishableKey,
 proxyUrl: resolvedProxyUrl,
Expand All@@ -114,13 +119,22 @@ export const withClerkMiddleware = (options: ClerkFastifyOptions) => {

 const locationHeader = requestState.headers.get(constants.Headers.Location);
 if (locationHeader) {
 return reply.code(307).send();
 } else if (requestState.status === AuthStatus.Handshake) {
 // Development instances cannot establish auth state without the dev browser handshake.
 const isDevBrowserHandshake =
 requestState.reason === 'dev-browser-missing' || requestState.reason === 'dev-browser-sync';
 if (enableHandshake || isDevBrowserHandshake) {
 return reply.code(307).send();
 }
 reply.removeHeader(constants.Headers.Location);
 reply.removeHeader(constants.Headers.CacheControl);
 } else if (enableHandshake && requestState.status === AuthStatus.Handshake) {
 throw new Error('Clerk: handshake status without redirect');
 }

 // A skipped handshake redirect leaves a handshake state whose toAuth() is null.
 // @ts-expect-error Inject auth so getAuth can read it
 fastifyRequest.auth = requestState.toAuth();
 fastifyRequest.auth =
 requestState.toAuth() ?? signedOutAuthObject({ reason: requestState.reason, message: requestState.message });
 fastifyRequest.clerk = clerkClient;
 };
};
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