fix(mcp): auth-type handling, OAuth-pending UX, safe diagnostics + HTTP/2 by waleedlatif1 · Pull Request #5757 · simstudioai/sim

waleedlatif1 · 2026-07-18T19:03:16Z

Summary

Minimal, focused set of MCP client fixes — the genuinely-good changes carved out of #5754 (whose large ordered-publication consistency layer was reverted as disproportionate; see below). Two clean commits, no fencing/CAS machinery.

Auth-type classification — a non-OAuth UnauthorizedError is now classified as an auth failure instead of an OAuth redirect, so static-bearer servers that merely advertise OAuth stop being diverted into the OAuth flow (fixes the class of server that couldn't connect, [BUG] MCP server "discover" step ignores configured static Authorization header, always requires OAuth #5665).
OAuth switch resets status — switching a server to OAuth now resets it to disconnected (it hasn't completed its auth flow), matching the create-path invariant, so it can't falsely read as connected.
OAuth-pending UX — the server list and refresh action surface "OAuth authorization required" instead of a generic "Not Connected".
DCR → 422 — OAuth servers that don't support dynamic client registration return an actionable 422.
Safe error diagnostics — MCP transport/connect logs redact messages/cause/session-ids via a shared getMcpSafeErrorDiagnostics.
HTTP/2 — the SSRF-pinned MCP fetch now negotiates h2 (MCP servers are commonly behind h2 fronts); pinning is unaffected. Default stays h1.1 for non-MCP callers.

Not in scope

This does not fix the dominant -32001 tools/list timeouts (connect-per-op with no connection reuse) — that's the next PR (turn-scoped connection reuse).

Type of Change

Bug fix
Improvement

Testing

416 MCP/security tests pass; tsc clean; biome clean; adversarial review passed.

Checklist

Code follows project style guidelines
Self-reviewed my changes
Tests added/updated and passing
No new warnings introduced
I confirm that I have read and agree to the terms outlined in the Contributor License Agreement (CLA)

vercel · 2026-07-18T19:03:18Z

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cursor · 2026-07-18T19:03:27Z

PR Summary

Medium Risk
Changes touch OAuth/auth classification, token revocation on config updates, and outbound HTTP transport (h2 + pinning); scope is well-tested but affects connection and credential handling paths.

Overview
Improves MCP auth correctness, settings messaging, and transport hardening without changing unrelated connection-reuse behavior.

Client & OAuth flow:UnauthorizedError is only treated as “authorization required” when authType is oauth, so header/token servers no longer get pushed into OAuth. OAuth start returns 422 with guidance when the auth server lacks dynamic client registration. Server updates that flip auth type (or add OAuth client ID) resetconnectionStatus to disconnected, clear lastError, revoke OAuth tokens when OAuth is turned off, and widen workspace cache invalidation (e.g. transport changes).

UX: Disconnected OAuth servers show “OAuth authorization required” in the list, detail status, and refresh action unless the refresh returned a concrete error (still Failed).

Logging & transport: Connect/transport/tools/list logs use getMcpSafeErrorDiagnostics (redacted structural fields, no messages/session IDs). The live MCP transport uses createPinnedMcpFetch with optional HTTP/2 (allowH2) while keeping IP pinning; the undici Agent is destroyed on failed connect and disconnect to avoid h2 socket leaks.

^{Reviewed by Cursor Bugbot for commit b856239. Configure here.}

greptile-apps · 2026-07-18T19:05:45Z

Greptile Summary

This PR improves MCP authentication, OAuth handling, diagnostics, and transport behavior. The main changes are:

Classify static-token authorization failures separately from OAuth redirects.
Reset connection state and clear OAuth credentials when authentication changes.
Show clearer OAuth authorization messages in server settings.
Return an actionable response when dynamic client registration is unsupported.
Redact MCP error diagnostics and omit unsafe error text.
Enable HTTP/2 for long-lived pinned MCP transports and close their Agents.

Confidence Score: 5/5

This looks safe to merge.

The reported authentication-state and OAuth-cleanup paths are addressed.
Pinned HTTP/2 transport resources are closed on disconnect and failed connection paths.
Error logs no longer include untrusted message text or session identifiers.
No blocking issues were found in the updated code.

Important Files Changed

Filename	Overview
apps/sim/lib/mcp/orchestration/server-lifecycle.ts	Resets stale connection state, cleans up OAuth credentials, and invalidates cached server state when authentication changes.
apps/sim/lib/mcp/client.ts	Separates static authentication failures from OAuth redirects, sanitizes diagnostics, and closes pinned transport resources.
apps/sim/lib/mcp/pinned-fetch.ts	Enables HTTP/2 for long-lived MCP transports and exposes an Agent cleanup handle.
apps/sim/lib/core/security/input-validation.server.ts	Adds optional HTTP/2 negotiation while preserving pinned address resolution and the existing HTTP/1.1 default.
apps/sim/lib/mcp/error-diagnostics.ts	Provides bounded and redacted structural diagnostics without credential-bearing messages or causes.

_{Reviews (5): Last reviewed commit: "fix(mcp): make pinned Agent teardown ide..." | Re-trigger Greptile}

waleedlatif1 · 2026-07-18T19:21:57Z

@greptile

waleedlatif1 · 2026-07-18T19:21:58Z

@cursor review

waleedlatif1 · 2026-07-18T19:30:34Z

@greptile

waleedlatif1 · 2026-07-18T19:30:35Z

@cursor review

waleedlatif1 · 2026-07-18T19:56:45Z

@greptile

waleedlatif1 · 2026-07-18T19:56:46Z

@cursor review

MCP servers are commonly behind HTTP/2 fronts (CDNs, cloud LBs), but the SSRF-pinned undici Agent is HTTP/1.1-only unless it opts into h2 via ALPN. Add an allowH2 option to createPinnedFetch (default false, so LLM-provider callers are unchanged) and centralize the MCP h2 decision in one createPinnedMcpFetch routed through the transport, OAuth probe, and SSRF-guarded fetch. Pinning is unaffected: the pinned lookup forces every connection to the resolved IP.

…r logging - Classify a non-OAuth UnauthorizedError as an auth failure instead of an OAuth redirect, so static-bearer servers that merely advertise OAuth stop being diverted into the OAuth flow (fixes the class of server that couldn't connect). - Reset a server to disconnected when it is switched to OAuth, so it can't falsely read as connected before completing its auth flow. - Surface OAuth-pending state as 'OAuth authorization required' in the server list and refresh action instead of a generic 'Not Connected'. - Return an actionable 422 for OAuth servers that don't support dynamic client registration. - Redact error messages/cause/session-ids from MCP transport/connect logs via a shared getMcpSafeErrorDiagnostics helper.

…ansport

… on auth-type change

…at client-id/secret setup

…oy on cancel/failed connect

waleedlatif1 · 2026-07-18T20:05:23Z

@greptile

waleedlatif1 · 2026-07-18T20:05:24Z

@cursor review

cursor

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit b856239. Configure here.}

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waleedlatif1 mentioned this pull request Jul 18, 2026
fix(mcp): stabilize authenticated tool discovery #5754
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cursorBot reviewed Jul 18, 2026
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Comment threadapps/sim/lib/mcp/orchestration/server-lifecycle.ts
Comment threadapps/sim/lib/mcp/client.ts
Comment threadapps/sim/lib/mcp/pinned-fetch.ts

waleedlatif1 force-pushed the mcp-connect-fixes branch from d498679 to 0424d18Compare July 18, 2026 19:21

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waleedlatif1 force-pushed the mcp-connect-fixes branch from 0424d18 to ae7f8b6Compare July 18, 2026 19:30

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Comment threadapps/sim/lib/mcp/client.ts

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waleedlatif1 added 5 commits July 18, 2026 13:04

fix(mcp): reset connection on any auth-type flip, scope h2 to live tr…
f085ef3
…ansport

fix(mcp): close pinned h2 Agent on disconnect and revoke OAuth tokens…
ba80c97
… on auth-type change

fix(mcp): release pinned Agent on failed connect and point DCR error …
4e3451b
…at client-id/secret setup

fix(mcp): make pinned Agent teardown idempotent to avoid double-destr…
b856239
…oy on cancel/failed connect

waleedlatif1 force-pushed the mcp-connect-fixes branch from c1c328e to b856239Compare July 18, 2026 20:04

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waleedlatif1 merged commit 32de415 into stagingJul 18, 2026
20 checks passed

waleedlatif1 deleted the mcp-connect-fixes branch July 18, 2026 20:19

waleedlatif1 mentioned this pull request Jul 19, 2026
v0.7.40: library, mcp hardening, pi code reviewer, gmail fix #5761
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waleedlatif1 commented Jul 18, 2026

Summary

Not in scope

Type of Change

Testing

Checklist

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PR Summary

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Greptile Summary

Confidence Score: 5/5

Important Files Changed

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