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fix(backend): preserve Set-Cookie headers through proxy#8162

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brkalow merged 6 commits into from
Mar 25, 2026
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fix(backend): preserve Set-Cookie headers through proxy #8162

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2808e54
Append set-cookie headers instead of set, supporting multiple headers…
brkalow Mar 25, 2026
f390667
fix(backend): preserve Set-Cookie headers and block SSRF in proxy
brkalow Mar 25, 2026
148923a
Apply suggestion from @brkalow
brkalow Mar 25, 2026
1883b8f
fix(backend): use string concatenation for FAPI URL to prevent SSRF b…
brkalow Mar 25, 2026
253ef98
Apply suggestion from @brkalow
brkalow Mar 25, 2026
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brkalow Mar 25, 2026
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5 changes: 5 additions & 0 deletions .changeset/warm-clubs-watch.md
View file
Open in desktop
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,5 @@
---
'@clerk/backend': patch
---

Fix an issue where multiple `set-cookie` headers were being dropped by the frontend API proxy.
43 changes: 43 additions & 0 deletions packages/backend/src/__tests__/proxy.test.ts
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -148,6 +148,22 @@ describe('proxy', () => {
expect(body.errors[0].code).toBe('proxy_path_mismatch');
});

it('does not follow protocol-relative paths', async () => {
const mockResponse = new Response('{}', { status: 200 });
mockFetch.mockResolvedValueOnce(mockResponse);

const request = new Request('https://example.com/__clerk//evil.com/steal');

await clerkFrontendApiProxy(request, {
publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
secretKey: 'sk_test_xxx',
});

// String concatenation keeps the host as FAPI, not evil.com
const fetchedUrl = new URL(mockFetch.mock.calls[0][0] as string);
expect(fetchedUrl.host).toBe('frontend-api.clerk.dev');
});

it('forwards GET request to FAPI with correct headers', async () => {
const mockResponse = new Response(JSON.stringify({ client: {} }), {
status: 200,
Expand DownExpand Up@@ -525,6 +541,33 @@ describe('proxy', () => {
expect(response.headers.get('Content-Type')).toBe('application/javascript');
});

it('preserves multiple Set-Cookie headers from FAPI response', async () => {
const headers = new Headers();
headers.append('Set-Cookie', '__client=abc123; Path=/; HttpOnly; Secure');
headers.append('Set-Cookie', '__client_uat=1234567890; Path=/; Secure');
headers.append('Set-Cookie', '__session=xyz789; Path=/; HttpOnly; Secure');
headers.append('Content-Type', 'application/json');

const mockResponse = new Response(JSON.stringify({ client: {} }), {
status: 200,
headers,
});
mockFetch.mockResolvedValue(mockResponse);

const request = new Request('https://example.com/__clerk/v1/client');

const response = await clerkFrontendApiProxy(request, {
publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
secretKey: 'sk_test_xxx',
});

const setCookies = response.headers.getSetCookie();
expect(setCookies).toHaveLength(3);
expect(setCookies).toContain('__client=abc123; Path=/; HttpOnly; Secure');
expect(setCookies).toContain('__client_uat=1234567890; Path=/; Secure');
expect(setCookies).toContain('__session=xyz789; Path=/; HttpOnly; Secure');
});

it('preserves relative Location headers', async () => {
const mockResponse = new Response(null, {
status: 302,
Expand Down
18 changes: 14 additions & 4 deletions packages/backend/src/proxy.ts
View file
Open in desktop
Original file line numberDiff line numberDiff line change
Expand Up@@ -214,12 +214,19 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
);
}

// Derive the FAPI URL and construct the target URL
// Derive the FAPI URL and construct the target URL.
// Use string concatenation instead of `new URL(path, base)` to avoid
// protocol-relative resolution (e.g., "//evil.com" resolving to a different host).
const fapiBaseUrl = fapiUrlFromPublishableKey(publishableKey);
const fapiHost = new URL(fapiBaseUrl).host;
const targetPath = requestUrl.pathname.slice(proxyPath.length) || '/';
const targetUrl = new URL(targetPath, fapiBaseUrl);
const targetUrl = new URL(`${fapiBaseUrl}${targetPath}`);
targetUrl.search = requestUrl.search;

if (targetUrl.host !== fapiHost) {
return createErrorResponse('proxy_request_failed', 'Resolved target does not match the expected host', 400);
}

// Build headers for the proxied request
const headers = new Headers();

Expand All@@ -239,7 +246,6 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
headers.set('Clerk-Secret-Key', secretKey);

// Set the host header to the FAPI host
const fapiHost = new URL(fapiBaseUrl).host;
headers.set('Host', fapiHost);

// Request uncompressed responses to avoid a double compression pass.
Expand DownExpand Up@@ -288,7 +294,11 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
response.headers.forEach((value, key) => {
const lower = key.toLowerCase();
if (!HOP_BY_HOP_HEADERS.includes(lower) && !RESPONSE_HEADERS_TO_STRIP.includes(lower)) {
responseHeaders.set(key, value);
if (lower === 'set-cookie') {
responseHeaders.append(key, value);
} else {
responseHeaders.set(key, value);
}
Comment thread
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}
});

Expand Down
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, '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" + '
fix(backend): preserve Set-Cookie headers through proxy by brkalow · Pull Request #8162 · clerk/javascript · GitHub
Skip to content
fix(backend): preserve Set-Cookie headers through proxy#8162

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 Merged

brkalow
merged 6 commits into

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Mar 25, 2026
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fix(backend): preserve Set-Cookie headers through proxy
#8162
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2808e54

Append set-cookie headers instead of set, supporting multiple headers…


brkalow Mar 25, 2026
f390667

fix(backend): preserve Set-Cookie headers and block SSRF in proxy


brkalow Mar 25, 2026
148923a

Apply suggestion from @brkalow


brkalow Mar 25, 2026
1883b8f

fix(backend): use string concatenation for FAPI URL to prevent SSRF b…


brkalow Mar 25, 2026
253ef98

Apply suggestion from @brkalow


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21a5805

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5 changes: 5 additions & 0 deletions
.changeset/warm-clubs-watch.md

View file


Open in desktop

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

Fix an issue where multiple `set-cookie` headers were being dropped by the frontend API proxy.

43 changes: 43 additions & 0 deletions
packages/backend/src/__tests__/proxy.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -148,6 +148,22 @@ describe('proxy', () => {
 expect(body.errors[0].code).toBe('proxy_path_mismatch');
 });

 it('does not follow protocol-relative paths', async () => {
 const mockResponse = new Response('{}', { status: 200 });
 mockFetch.mockResolvedValueOnce(mockResponse);

 const request = new Request('https://example.com/__clerk//evil.com/steal');

 await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 // String concatenation keeps the host as FAPI, not evil.com
 const fetchedUrl = new URL(mockFetch.mock.calls[0][0] as string);
 expect(fetchedUrl.host).toBe('frontend-api.clerk.dev');
 });

 it('forwards GET request to FAPI with correct headers', async () => {
 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
Expand DownExpand Up@@ -525,6 +541,33 @@ describe('proxy', () => {
 expect(response.headers.get('Content-Type')).toBe('application/javascript');
 });

 it('preserves multiple Set-Cookie headers from FAPI response', async () => {
 const headers = new Headers();
 headers.append('Set-Cookie', '__client=abc123; Path=/; HttpOnly; Secure');
 headers.append('Set-Cookie', '__client_uat=1234567890; Path=/; Secure');
 headers.append('Set-Cookie', '__session=xyz789; Path=/; HttpOnly; Secure');
 headers.append('Content-Type', 'application/json');

 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
 headers,
 });
 mockFetch.mockResolvedValue(mockResponse);

 const request = new Request('https://example.com/__clerk/v1/client');

 const response = await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 const setCookies = response.headers.getSetCookie();
 expect(setCookies).toHaveLength(3);
 expect(setCookies).toContain('__client=abc123; Path=/; HttpOnly; Secure');
 expect(setCookies).toContain('__client_uat=1234567890; Path=/; Secure');
 expect(setCookies).toContain('__session=xyz789; Path=/; HttpOnly; Secure');
 });

 it('preserves relative Location headers', async () => {
 const mockResponse = new Response(null, {
 status: 302,
Expand Down

18 changes: 14 additions & 4 deletions
packages/backend/src/proxy.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -214,12 +214,19 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 );
 }

 // Derive the FAPI URL and construct the target URL
 // Derive the FAPI URL and construct the target URL.
 // Use string concatenation instead of `new URL(path, base)` to avoid
 // protocol-relative resolution (e.g., "//evil.com" resolving to a different host).
 const fapiBaseUrl = fapiUrlFromPublishableKey(publishableKey);
 const fapiHost = new URL(fapiBaseUrl).host;
 const targetPath = requestUrl.pathname.slice(proxyPath.length) || '/';
 const targetUrl = new URL(targetPath, fapiBaseUrl);
 const targetUrl = new URL(`${fapiBaseUrl}${targetPath}`);
 targetUrl.search = requestUrl.search;

 if (targetUrl.host !== fapiHost) {
 return createErrorResponse('proxy_request_failed', 'Resolved target does not match the expected host', 400);
 }

 // Build headers for the proxied request
 const headers = new Headers();

Expand All@@ -239,7 +246,6 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 headers.set('Clerk-Secret-Key', secretKey);

 // Set the host header to the FAPI host
 const fapiHost = new URL(fapiBaseUrl).host;
 headers.set('Host', fapiHost);

 // Request uncompressed responses to avoid a double compression pass.
Expand DownExpand Up@@ -288,7 +294,11 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 response.headers.forEach((value, key) => {
 const lower = key.toLowerCase();
 if (!HOP_BY_HOP_HEADERS.includes(lower) && !RESPONSE_HEADERS_TO_STRIP.includes(lower)) {
 responseHeaders.set(key, value);
 if (lower === 'set-cookie') {
 responseHeaders.append(key, value);
 } else {
 responseHeaders.set(key, value);
 }
Comment thread
brkalow marked this conversation as resolved.

Comment thread
brkalow marked this conversation as resolved.

 }
 });

Expand Down
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Force GitHub README to respect dark mode
(function() {
var style = document.createElement('style');
style.textContent = '
.markdown-body {
color-scheme: dark light;
}
.markdown-body pre { background: #161b22 !important; }
.markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }
.markdown-body table th, .markdown-body table td { border-color: #30363d !important; }
.markdown-body img { background: #0d1117; }
.markdown-body blockquote { border-left-color: #8b949e; }
.markdown-body hr { border-color: #30363d; }
';
document.head.appendChild(style);
})();
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
fix(backend): preserve Set-Cookie headers through proxy by brkalow · Pull Request #8162 · clerk/javascript · GitHub
Skip to content
fix(backend): preserve Set-Cookie headers through proxy#8162

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 Merged

brkalow
merged 6 commits into

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Mar 25, 2026
 Merged


fix(backend): preserve Set-Cookie headers through proxy
#8162
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2808e54

Append set-cookie headers instead of set, supporting multiple headers…


brkalow Mar 25, 2026
f390667

fix(backend): preserve Set-Cookie headers and block SSRF in proxy


brkalow Mar 25, 2026
148923a

Apply suggestion from @brkalow


brkalow Mar 25, 2026
1883b8f

fix(backend): use string concatenation for FAPI URL to prevent SSRF b…


brkalow Mar 25, 2026
253ef98

Apply suggestion from @brkalow


brkalow Mar 25, 2026
21a5805

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brkalow Mar 25, 2026

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5 changes: 5 additions & 0 deletions
.changeset/warm-clubs-watch.md

View file


Open in desktop

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

Fix an issue where multiple `set-cookie` headers were being dropped by the frontend API proxy.

43 changes: 43 additions & 0 deletions
packages/backend/src/__tests__/proxy.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -148,6 +148,22 @@ describe('proxy', () => {
 expect(body.errors[0].code).toBe('proxy_path_mismatch');
 });

 it('does not follow protocol-relative paths', async () => {
 const mockResponse = new Response('{}', { status: 200 });
 mockFetch.mockResolvedValueOnce(mockResponse);

 const request = new Request('https://example.com/__clerk//evil.com/steal');

 await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 // String concatenation keeps the host as FAPI, not evil.com
 const fetchedUrl = new URL(mockFetch.mock.calls[0][0] as string);
 expect(fetchedUrl.host).toBe('frontend-api.clerk.dev');
 });

 it('forwards GET request to FAPI with correct headers', async () => {
 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
Expand DownExpand Up@@ -525,6 +541,33 @@ describe('proxy', () => {
 expect(response.headers.get('Content-Type')).toBe('application/javascript');
 });

 it('preserves multiple Set-Cookie headers from FAPI response', async () => {
 const headers = new Headers();
 headers.append('Set-Cookie', '__client=abc123; Path=/; HttpOnly; Secure');
 headers.append('Set-Cookie', '__client_uat=1234567890; Path=/; Secure');
 headers.append('Set-Cookie', '__session=xyz789; Path=/; HttpOnly; Secure');
 headers.append('Content-Type', 'application/json');

 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
 headers,
 });
 mockFetch.mockResolvedValue(mockResponse);

 const request = new Request('https://example.com/__clerk/v1/client');

 const response = await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 const setCookies = response.headers.getSetCookie();
 expect(setCookies).toHaveLength(3);
 expect(setCookies).toContain('__client=abc123; Path=/; HttpOnly; Secure');
 expect(setCookies).toContain('__client_uat=1234567890; Path=/; Secure');
 expect(setCookies).toContain('__session=xyz789; Path=/; HttpOnly; Secure');
 });

 it('preserves relative Location headers', async () => {
 const mockResponse = new Response(null, {
 status: 302,
Expand Down

18 changes: 14 additions & 4 deletions
packages/backend/src/proxy.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -214,12 +214,19 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 );
 }

 // Derive the FAPI URL and construct the target URL
 // Derive the FAPI URL and construct the target URL.
 // Use string concatenation instead of `new URL(path, base)` to avoid
 // protocol-relative resolution (e.g., "//evil.com" resolving to a different host).
 const fapiBaseUrl = fapiUrlFromPublishableKey(publishableKey);
 const fapiHost = new URL(fapiBaseUrl).host;
 const targetPath = requestUrl.pathname.slice(proxyPath.length) || '/';
 const targetUrl = new URL(targetPath, fapiBaseUrl);
 const targetUrl = new URL(`${fapiBaseUrl}${targetPath}`);
 targetUrl.search = requestUrl.search;

 if (targetUrl.host !== fapiHost) {
 return createErrorResponse('proxy_request_failed', 'Resolved target does not match the expected host', 400);
 }

 // Build headers for the proxied request
 const headers = new Headers();

Expand All@@ -239,7 +246,6 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 headers.set('Clerk-Secret-Key', secretKey);

 // Set the host header to the FAPI host
 const fapiHost = new URL(fapiBaseUrl).host;
 headers.set('Host', fapiHost);

 // Request uncompressed responses to avoid a double compression pass.
Expand DownExpand Up@@ -288,7 +294,11 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 response.headers.forEach((value, key) => {
 const lower = key.toLowerCase();
 if (!HOP_BY_HOP_HEADERS.includes(lower) && !RESPONSE_HEADERS_TO_STRIP.includes(lower)) {
 responseHeaders.set(key, value);
 if (lower === 'set-cookie') {
 responseHeaders.append(key, value);
 } else {
 responseHeaders.set(key, value);
 }
Comment thread
brkalow marked this conversation as resolved.

Comment thread
brkalow marked this conversation as resolved.

 }
 });

Expand Down
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, '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);
// Re-highlight on dynamic content
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
fix(backend): preserve Set-Cookie headers through proxy by brkalow · Pull Request #8162 · clerk/javascript · GitHub
Skip to content
fix(backend): preserve Set-Cookie headers through proxy#8162

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 Merged

brkalow
merged 6 commits into

from

Mar 25, 2026
 Merged


fix(backend): preserve Set-Cookie headers through proxy
#8162
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2808e54

Append set-cookie headers instead of set, supporting multiple headers…


brkalow Mar 25, 2026
f390667

fix(backend): preserve Set-Cookie headers and block SSRF in proxy


brkalow Mar 25, 2026
148923a

Apply suggestion from @brkalow


brkalow Mar 25, 2026
1883b8f

fix(backend): use string concatenation for FAPI URL to prevent SSRF b…


brkalow Mar 25, 2026
253ef98

Apply suggestion from @brkalow


brkalow Mar 25, 2026
21a5805

Apply suggestion from @brkalow


brkalow Mar 25, 2026

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5 changes: 5 additions & 0 deletions
.changeset/warm-clubs-watch.md

View file


Open in desktop

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

Fix an issue where multiple `set-cookie` headers were being dropped by the frontend API proxy.

43 changes: 43 additions & 0 deletions
packages/backend/src/__tests__/proxy.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -148,6 +148,22 @@ describe('proxy', () => {
 expect(body.errors[0].code).toBe('proxy_path_mismatch');
 });

 it('does not follow protocol-relative paths', async () => {
 const mockResponse = new Response('{}', { status: 200 });
 mockFetch.mockResolvedValueOnce(mockResponse);

 const request = new Request('https://example.com/__clerk//evil.com/steal');

 await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 // String concatenation keeps the host as FAPI, not evil.com
 const fetchedUrl = new URL(mockFetch.mock.calls[0][0] as string);
 expect(fetchedUrl.host).toBe('frontend-api.clerk.dev');
 });

 it('forwards GET request to FAPI with correct headers', async () => {
 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
Expand DownExpand Up@@ -525,6 +541,33 @@ describe('proxy', () => {
 expect(response.headers.get('Content-Type')).toBe('application/javascript');
 });

 it('preserves multiple Set-Cookie headers from FAPI response', async () => {
 const headers = new Headers();
 headers.append('Set-Cookie', '__client=abc123; Path=/; HttpOnly; Secure');
 headers.append('Set-Cookie', '__client_uat=1234567890; Path=/; Secure');
 headers.append('Set-Cookie', '__session=xyz789; Path=/; HttpOnly; Secure');
 headers.append('Content-Type', 'application/json');

 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
 headers,
 });
 mockFetch.mockResolvedValue(mockResponse);

 const request = new Request('https://example.com/__clerk/v1/client');

 const response = await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 const setCookies = response.headers.getSetCookie();
 expect(setCookies).toHaveLength(3);
 expect(setCookies).toContain('__client=abc123; Path=/; HttpOnly; Secure');
 expect(setCookies).toContain('__client_uat=1234567890; Path=/; Secure');
 expect(setCookies).toContain('__session=xyz789; Path=/; HttpOnly; Secure');
 });

 it('preserves relative Location headers', async () => {
 const mockResponse = new Response(null, {
 status: 302,
Expand Down

18 changes: 14 additions & 4 deletions
packages/backend/src/proxy.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -214,12 +214,19 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 );
 }

 // Derive the FAPI URL and construct the target URL
 // Derive the FAPI URL and construct the target URL.
 // Use string concatenation instead of `new URL(path, base)` to avoid
 // protocol-relative resolution (e.g., "//evil.com" resolving to a different host).
 const fapiBaseUrl = fapiUrlFromPublishableKey(publishableKey);
 const fapiHost = new URL(fapiBaseUrl).host;
 const targetPath = requestUrl.pathname.slice(proxyPath.length) || '/';
 const targetUrl = new URL(targetPath, fapiBaseUrl);
 const targetUrl = new URL(`${fapiBaseUrl}${targetPath}`);
 targetUrl.search = requestUrl.search;

 if (targetUrl.host !== fapiHost) {
 return createErrorResponse('proxy_request_failed', 'Resolved target does not match the expected host', 400);
 }

 // Build headers for the proxied request
 const headers = new Headers();

Expand All@@ -239,7 +246,6 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 headers.set('Clerk-Secret-Key', secretKey);

 // Set the host header to the FAPI host
 const fapiHost = new URL(fapiBaseUrl).host;
 headers.set('Host', fapiHost);

 // Request uncompressed responses to avoid a double compression pass.
Expand DownExpand Up@@ -288,7 +294,11 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 response.headers.forEach((value, key) => {
 const lower = key.toLowerCase();
 if (!HOP_BY_HOP_HEADERS.includes(lower) && !RESPONSE_HEADERS_TO_STRIP.includes(lower)) {
 responseHeaders.set(key, value);
 if (lower === 'set-cookie') {
 responseHeaders.append(key, value);
 } else {
 responseHeaders.set(key, value);
 }
Comment thread
brkalow marked this conversation as resolved.

Comment thread
brkalow marked this conversation as resolved.

 }
 });

Expand Down
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" + '
fix(backend): preserve Set-Cookie headers through proxy by brkalow · Pull Request #8162 · clerk/javascript · GitHub
Skip to content
fix(backend): preserve Set-Cookie headers through proxy#8162

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brkalow
merged 6 commits into

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Mar 25, 2026
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fix(backend): preserve Set-Cookie headers through proxy
#8162
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2808e54

Append set-cookie headers instead of set, supporting multiple headers…


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f390667

fix(backend): preserve Set-Cookie headers and block SSRF in proxy


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148923a

Apply suggestion from @brkalow


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1883b8f

fix(backend): use string concatenation for FAPI URL to prevent SSRF b…


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253ef98

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5 changes: 5 additions & 0 deletions
.changeset/warm-clubs-watch.md

View file


Open in desktop

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

Fix an issue where multiple `set-cookie` headers were being dropped by the frontend API proxy.

43 changes: 43 additions & 0 deletions
packages/backend/src/__tests__/proxy.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -148,6 +148,22 @@ describe('proxy', () => {
 expect(body.errors[0].code).toBe('proxy_path_mismatch');
 });

 it('does not follow protocol-relative paths', async () => {
 const mockResponse = new Response('{}', { status: 200 });
 mockFetch.mockResolvedValueOnce(mockResponse);

 const request = new Request('https://example.com/__clerk//evil.com/steal');

 await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 // String concatenation keeps the host as FAPI, not evil.com
 const fetchedUrl = new URL(mockFetch.mock.calls[0][0] as string);
 expect(fetchedUrl.host).toBe('frontend-api.clerk.dev');
 });

 it('forwards GET request to FAPI with correct headers', async () => {
 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
Expand DownExpand Up@@ -525,6 +541,33 @@ describe('proxy', () => {
 expect(response.headers.get('Content-Type')).toBe('application/javascript');
 });

 it('preserves multiple Set-Cookie headers from FAPI response', async () => {
 const headers = new Headers();
 headers.append('Set-Cookie', '__client=abc123; Path=/; HttpOnly; Secure');
 headers.append('Set-Cookie', '__client_uat=1234567890; Path=/; Secure');
 headers.append('Set-Cookie', '__session=xyz789; Path=/; HttpOnly; Secure');
 headers.append('Content-Type', 'application/json');

 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
 headers,
 });
 mockFetch.mockResolvedValue(mockResponse);

 const request = new Request('https://example.com/__clerk/v1/client');

 const response = await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 const setCookies = response.headers.getSetCookie();
 expect(setCookies).toHaveLength(3);
 expect(setCookies).toContain('__client=abc123; Path=/; HttpOnly; Secure');
 expect(setCookies).toContain('__client_uat=1234567890; Path=/; Secure');
 expect(setCookies).toContain('__session=xyz789; Path=/; HttpOnly; Secure');
 });

 it('preserves relative Location headers', async () => {
 const mockResponse = new Response(null, {
 status: 302,
Expand Down

18 changes: 14 additions & 4 deletions
packages/backend/src/proxy.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -214,12 +214,19 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 );
 }

 // Derive the FAPI URL and construct the target URL
 // Derive the FAPI URL and construct the target URL.
 // Use string concatenation instead of `new URL(path, base)` to avoid
 // protocol-relative resolution (e.g., "//evil.com" resolving to a different host).
 const fapiBaseUrl = fapiUrlFromPublishableKey(publishableKey);
 const fapiHost = new URL(fapiBaseUrl).host;
 const targetPath = requestUrl.pathname.slice(proxyPath.length) || '/';
 const targetUrl = new URL(targetPath, fapiBaseUrl);
 const targetUrl = new URL(`${fapiBaseUrl}${targetPath}`);
 targetUrl.search = requestUrl.search;

 if (targetUrl.host !== fapiHost) {
 return createErrorResponse('proxy_request_failed', 'Resolved target does not match the expected host', 400);
 }

 // Build headers for the proxied request
 const headers = new Headers();

Expand All@@ -239,7 +246,6 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 headers.set('Clerk-Secret-Key', secretKey);

 // Set the host header to the FAPI host
 const fapiHost = new URL(fapiBaseUrl).host;
 headers.set('Host', fapiHost);

 // Request uncompressed responses to avoid a double compression pass.
Expand DownExpand Up@@ -288,7 +294,11 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 response.headers.forEach((value, key) => {
 const lower = key.toLowerCase();
 if (!HOP_BY_HOP_HEADERS.includes(lower) && !RESPONSE_HEADERS_TO_STRIP.includes(lower)) {
 responseHeaders.set(key, value);
 if (lower === 'set-cookie') {
 responseHeaders.append(key, value);
 } else {
 responseHeaders.set(key, value);
 }
Comment thread
brkalow marked this conversation as resolved.

Comment thread
brkalow marked this conversation as resolved.

 }
 });

Expand Down
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('^' + ".*" + '
fix(backend): preserve Set-Cookie headers through proxy by brkalow · Pull Request #8162 · clerk/javascript · GitHub
Skip to content
fix(backend): preserve Set-Cookie headers through proxy#8162

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 Merged

brkalow
merged 6 commits into

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Mar 25, 2026
 Merged


fix(backend): preserve Set-Cookie headers through proxy
#8162
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2808e54

Append set-cookie headers instead of set, supporting multiple headers…


brkalow Mar 25, 2026
f390667

fix(backend): preserve Set-Cookie headers and block SSRF in proxy


brkalow Mar 25, 2026
148923a

Apply suggestion from @brkalow


brkalow Mar 25, 2026
1883b8f

fix(backend): use string concatenation for FAPI URL to prevent SSRF b…


brkalow Mar 25, 2026
253ef98

Apply suggestion from @brkalow


brkalow Mar 25, 2026
21a5805

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5 changes: 5 additions & 0 deletions
.changeset/warm-clubs-watch.md

View file


Open in desktop

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

Fix an issue where multiple `set-cookie` headers were being dropped by the frontend API proxy.

43 changes: 43 additions & 0 deletions
packages/backend/src/__tests__/proxy.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -148,6 +148,22 @@ describe('proxy', () => {
 expect(body.errors[0].code).toBe('proxy_path_mismatch');
 });

 it('does not follow protocol-relative paths', async () => {
 const mockResponse = new Response('{}', { status: 200 });
 mockFetch.mockResolvedValueOnce(mockResponse);

 const request = new Request('https://example.com/__clerk//evil.com/steal');

 await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 // String concatenation keeps the host as FAPI, not evil.com
 const fetchedUrl = new URL(mockFetch.mock.calls[0][0] as string);
 expect(fetchedUrl.host).toBe('frontend-api.clerk.dev');
 });

 it('forwards GET request to FAPI with correct headers', async () => {
 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
Expand DownExpand Up@@ -525,6 +541,33 @@ describe('proxy', () => {
 expect(response.headers.get('Content-Type')).toBe('application/javascript');
 });

 it('preserves multiple Set-Cookie headers from FAPI response', async () => {
 const headers = new Headers();
 headers.append('Set-Cookie', '__client=abc123; Path=/; HttpOnly; Secure');
 headers.append('Set-Cookie', '__client_uat=1234567890; Path=/; Secure');
 headers.append('Set-Cookie', '__session=xyz789; Path=/; HttpOnly; Secure');
 headers.append('Content-Type', 'application/json');

 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
 headers,
 });
 mockFetch.mockResolvedValue(mockResponse);

 const request = new Request('https://example.com/__clerk/v1/client');

 const response = await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 const setCookies = response.headers.getSetCookie();
 expect(setCookies).toHaveLength(3);
 expect(setCookies).toContain('__client=abc123; Path=/; HttpOnly; Secure');
 expect(setCookies).toContain('__client_uat=1234567890; Path=/; Secure');
 expect(setCookies).toContain('__session=xyz789; Path=/; HttpOnly; Secure');
 });

 it('preserves relative Location headers', async () => {
 const mockResponse = new Response(null, {
 status: 302,
Expand Down

18 changes: 14 additions & 4 deletions
packages/backend/src/proxy.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -214,12 +214,19 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 );
 }

 // Derive the FAPI URL and construct the target URL
 // Derive the FAPI URL and construct the target URL.
 // Use string concatenation instead of `new URL(path, base)` to avoid
 // protocol-relative resolution (e.g., "//evil.com" resolving to a different host).
 const fapiBaseUrl = fapiUrlFromPublishableKey(publishableKey);
 const fapiHost = new URL(fapiBaseUrl).host;
 const targetPath = requestUrl.pathname.slice(proxyPath.length) || '/';
 const targetUrl = new URL(targetPath, fapiBaseUrl);
 const targetUrl = new URL(`${fapiBaseUrl}${targetPath}`);
 targetUrl.search = requestUrl.search;

 if (targetUrl.host !== fapiHost) {
 return createErrorResponse('proxy_request_failed', 'Resolved target does not match the expected host', 400);
 }

 // Build headers for the proxied request
 const headers = new Headers();

Expand All@@ -239,7 +246,6 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 headers.set('Clerk-Secret-Key', secretKey);

 // Set the host header to the FAPI host
 const fapiHost = new URL(fapiBaseUrl).host;
 headers.set('Host', fapiHost);

 // Request uncompressed responses to avoid a double compression pass.
Expand DownExpand Up@@ -288,7 +294,11 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 response.headers.forEach((value, key) => {
 const lower = key.toLowerCase();
 if (!HOP_BY_HOP_HEADERS.includes(lower) && !RESPONSE_HEADERS_TO_STRIP.includes(lower)) {
 responseHeaders.set(key, value);
 if (lower === 'set-cookie') {
 responseHeaders.append(key, value);
 } else {
 responseHeaders.set(key, value);
 }
Comment thread
brkalow marked this conversation as resolved.

Comment thread
brkalow marked this conversation as resolved.

 }
 });

Expand Down
Loading

, 'i');
if (__m === '*' || __re.test(location.href)) {
// 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'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
fix(backend): preserve Set-Cookie headers through proxy by brkalow · Pull Request #8162 · clerk/javascript · GitHub
Skip to content
fix(backend): preserve Set-Cookie headers through proxy#8162

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Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

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

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 Merged

brkalow
merged 6 commits into

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Mar 25, 2026
 Merged


fix(backend): preserve Set-Cookie headers through proxy
#8162
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2808e54

Append set-cookie headers instead of set, supporting multiple headers…


brkalow Mar 25, 2026
f390667

fix(backend): preserve Set-Cookie headers and block SSRF in proxy


brkalow Mar 25, 2026
148923a

Apply suggestion from @brkalow


brkalow Mar 25, 2026
1883b8f

fix(backend): use string concatenation for FAPI URL to prevent SSRF b…


brkalow Mar 25, 2026
253ef98

Apply suggestion from @brkalow


brkalow Mar 25, 2026
21a5805

Apply suggestion from @brkalow


brkalow Mar 25, 2026

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5 changes: 5 additions & 0 deletions
.changeset/warm-clubs-watch.md

View file


Open in desktop

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

Fix an issue where multiple `set-cookie` headers were being dropped by the frontend API proxy.

43 changes: 43 additions & 0 deletions
packages/backend/src/__tests__/proxy.test.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -148,6 +148,22 @@ describe('proxy', () => {
 expect(body.errors[0].code).toBe('proxy_path_mismatch');
 });

 it('does not follow protocol-relative paths', async () => {
 const mockResponse = new Response('{}', { status: 200 });
 mockFetch.mockResolvedValueOnce(mockResponse);

 const request = new Request('https://example.com/__clerk//evil.com/steal');

 await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 // String concatenation keeps the host as FAPI, not evil.com
 const fetchedUrl = new URL(mockFetch.mock.calls[0][0] as string);
 expect(fetchedUrl.host).toBe('frontend-api.clerk.dev');
 });

 it('forwards GET request to FAPI with correct headers', async () => {
 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
Expand DownExpand Up@@ -525,6 +541,33 @@ describe('proxy', () => {
 expect(response.headers.get('Content-Type')).toBe('application/javascript');
 });

 it('preserves multiple Set-Cookie headers from FAPI response', async () => {
 const headers = new Headers();
 headers.append('Set-Cookie', '__client=abc123; Path=/; HttpOnly; Secure');
 headers.append('Set-Cookie', '__client_uat=1234567890; Path=/; Secure');
 headers.append('Set-Cookie', '__session=xyz789; Path=/; HttpOnly; Secure');
 headers.append('Content-Type', 'application/json');

 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
 headers,
 });
 mockFetch.mockResolvedValue(mockResponse);

 const request = new Request('https://example.com/__clerk/v1/client');

 const response = await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 const setCookies = response.headers.getSetCookie();
 expect(setCookies).toHaveLength(3);
 expect(setCookies).toContain('__client=abc123; Path=/; HttpOnly; Secure');
 expect(setCookies).toContain('__client_uat=1234567890; Path=/; Secure');
 expect(setCookies).toContain('__session=xyz789; Path=/; HttpOnly; Secure');
 });

 it('preserves relative Location headers', async () => {
 const mockResponse = new Response(null, {
 status: 302,
Expand Down

18 changes: 14 additions & 4 deletions
packages/backend/src/proxy.ts

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -214,12 +214,19 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 );
 }

 // Derive the FAPI URL and construct the target URL
 // Derive the FAPI URL and construct the target URL.
 // Use string concatenation instead of `new URL(path, base)` to avoid
 // protocol-relative resolution (e.g., "//evil.com" resolving to a different host).
 const fapiBaseUrl = fapiUrlFromPublishableKey(publishableKey);
 const fapiHost = new URL(fapiBaseUrl).host;
 const targetPath = requestUrl.pathname.slice(proxyPath.length) || '/';
 const targetUrl = new URL(targetPath, fapiBaseUrl);
 const targetUrl = new URL(`${fapiBaseUrl}${targetPath}`);
 targetUrl.search = requestUrl.search;

 if (targetUrl.host !== fapiHost) {
 return createErrorResponse('proxy_request_failed', 'Resolved target does not match the expected host', 400);
 }

 // Build headers for the proxied request
 const headers = new Headers();

Expand All@@ -239,7 +246,6 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 headers.set('Clerk-Secret-Key', secretKey);

 // Set the host header to the FAPI host
 const fapiHost = new URL(fapiBaseUrl).host;
 headers.set('Host', fapiHost);

 // Request uncompressed responses to avoid a double compression pass.
Expand DownExpand Up@@ -288,7 +294,11 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 response.headers.forEach((value, key) => {
 const lower = key.toLowerCase();
 if (!HOP_BY_HOP_HEADERS.includes(lower) && !RESPONSE_HEADERS_TO_STRIP.includes(lower)) {
 responseHeaders.set(key, value);
 if (lower === 'set-cookie') {
 responseHeaders.append(key, value);
 } else {
 responseHeaders.set(key, value);
 }
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, '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');
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}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
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})();
fix(backend): preserve Set-Cookie headers through proxy by brkalow · Pull Request #8162 · clerk/javascript · GitHub
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fix(backend): preserve Set-Cookie headers through proxy#8162

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brkalow
merged 6 commits into

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Mar 25, 2026
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fix(backend): preserve Set-Cookie headers through proxy
#8162
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2808e54

Append set-cookie headers instead of set, supporting multiple headers…


brkalow Mar 25, 2026
f390667

fix(backend): preserve Set-Cookie headers and block SSRF in proxy


brkalow Mar 25, 2026
148923a

Apply suggestion from @brkalow


brkalow Mar 25, 2026
1883b8f

fix(backend): use string concatenation for FAPI URL to prevent SSRF b…


brkalow Mar 25, 2026
253ef98

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5 changes: 5 additions & 0 deletions
.changeset/warm-clubs-watch.md

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

Fix an issue where multiple `set-cookie` headers were being dropped by the frontend API proxy.

43 changes: 43 additions & 0 deletions
packages/backend/src/__tests__/proxy.test.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -148,6 +148,22 @@ describe('proxy', () => {
 expect(body.errors[0].code).toBe('proxy_path_mismatch');
 });

 it('does not follow protocol-relative paths', async () => {
 const mockResponse = new Response('{}', { status: 200 });
 mockFetch.mockResolvedValueOnce(mockResponse);

 const request = new Request('https://example.com/__clerk//evil.com/steal');

 await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 // String concatenation keeps the host as FAPI, not evil.com
 const fetchedUrl = new URL(mockFetch.mock.calls[0][0] as string);
 expect(fetchedUrl.host).toBe('frontend-api.clerk.dev');
 });

 it('forwards GET request to FAPI with correct headers', async () => {
 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
Expand DownExpand Up@@ -525,6 +541,33 @@ describe('proxy', () => {
 expect(response.headers.get('Content-Type')).toBe('application/javascript');
 });

 it('preserves multiple Set-Cookie headers from FAPI response', async () => {
 const headers = new Headers();
 headers.append('Set-Cookie', '__client=abc123; Path=/; HttpOnly; Secure');
 headers.append('Set-Cookie', '__client_uat=1234567890; Path=/; Secure');
 headers.append('Set-Cookie', '__session=xyz789; Path=/; HttpOnly; Secure');
 headers.append('Content-Type', 'application/json');

 const mockResponse = new Response(JSON.stringify({ client: {} }), {
 status: 200,
 headers,
 });
 mockFetch.mockResolvedValue(mockResponse);

 const request = new Request('https://example.com/__clerk/v1/client');

 const response = await clerkFrontendApiProxy(request, {
 publishableKey: 'pk_test_Y2xlcmsuZXhhbXBsZS5jb20k',
 secretKey: 'sk_test_xxx',
 });

 const setCookies = response.headers.getSetCookie();
 expect(setCookies).toHaveLength(3);
 expect(setCookies).toContain('__client=abc123; Path=/; HttpOnly; Secure');
 expect(setCookies).toContain('__client_uat=1234567890; Path=/; Secure');
 expect(setCookies).toContain('__session=xyz789; Path=/; HttpOnly; Secure');
 });

 it('preserves relative Location headers', async () => {
 const mockResponse = new Response(null, {
 status: 302,
Expand Down

18 changes: 14 additions & 4 deletions
packages/backend/src/proxy.ts

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Original file line numberDiff line numberDiff line change
Expand Up@@ -214,12 +214,19 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 );
 }

 // Derive the FAPI URL and construct the target URL
 // Derive the FAPI URL and construct the target URL.
 // Use string concatenation instead of `new URL(path, base)` to avoid
 // protocol-relative resolution (e.g., "//evil.com" resolving to a different host).
 const fapiBaseUrl = fapiUrlFromPublishableKey(publishableKey);
 const fapiHost = new URL(fapiBaseUrl).host;
 const targetPath = requestUrl.pathname.slice(proxyPath.length) || '/';
 const targetUrl = new URL(targetPath, fapiBaseUrl);
 const targetUrl = new URL(`${fapiBaseUrl}${targetPath}`);
 targetUrl.search = requestUrl.search;

 if (targetUrl.host !== fapiHost) {
 return createErrorResponse('proxy_request_failed', 'Resolved target does not match the expected host', 400);
 }

 // Build headers for the proxied request
 const headers = new Headers();

Expand All@@ -239,7 +246,6 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 headers.set('Clerk-Secret-Key', secretKey);

 // Set the host header to the FAPI host
 const fapiHost = new URL(fapiBaseUrl).host;
 headers.set('Host', fapiHost);

 // Request uncompressed responses to avoid a double compression pass.
Expand DownExpand Up@@ -288,7 +294,11 @@ export async function clerkFrontendApiProxy(request: Request, options?: Frontend
 response.headers.forEach((value, key) => {
 const lower = key.toLowerCase();
 if (!HOP_BY_HOP_HEADERS.includes(lower) && !RESPONSE_HEADERS_TO_STRIP.includes(lower)) {
 responseHeaders.set(key, value);
 if (lower === 'set-cookie') {
 responseHeaders.append(key, value);
 } else {
 responseHeaders.set(key, value);
 }
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