fix: gate user-mode flows on caller user_id and skip temp token mint

[Pratham-Mishra04]

Summary

User-mode MCP auth flows were not properly scoped to the user who initiated them. Any authenticated SSO user holding a user-mode auth URL could view, start, or submit a flow bound to a different user, potentially planting their upstream credentials under that user's identity. This PR adds an identity gate to all user-mode flow endpoints and fixes the temp token minting logic that was causing legitimate users to receive 403s on their own flows.

Changes

• Added canAccessUserFlow helper that enforces caller user_id must match flow.UserID for user-mode flows; VK and session-mode flows remain intentionally shareable and pass through unchanged.
• Applied the identity gate to flowDetail, flowSubmit, and flowStart in both the OAuth sessions handler and the per-user headers handler, returning a 403 with a descriptive message when the check fails.
• Skipped temp token minting for user-mode flows in both InitiateUserSubmissionFlow and InitiateUserOAuthFlow. Minting a temp token routes requests through the temp-token middleware branch, which bypasses cookie resolution and leaves the caller user_id empty, causing the new identity gate to 403 even legitimate users.
• Updated the UI's 401 redirect to preserve the current path and query string as a goto parameter so users are returned to their original destination after logging in.

Type of change

• Bug fix
• Feature
• Refactor
• Documentation
• Chore/CI

Affected areas

• Core (Go)
• Transports (HTTP)
• Providers/Integrations
• Plugins
• UI (React)
• Docs

How to test

1. Create a user-mode MCP auth flow as User A and copy the auth URL.
2. Log in as User B and navigate to that URL — expect a 403 with "This authentication link is bound to a different user.".
3. Log in as User A and navigate to the same URL — expect normal flow behavior.
4. Verify VK-mode and session-mode flow URLs remain accessible across users.
5. Trigger a 401 response in the UI while on a non-login page and confirm the redirect lands on /login?goto=<original-path> and returns you there after login.

go test ./framework/... ./transports/...

cd ui
pnpm i
pnpm build

Breaking changes

• No

Security considerations

Without this gate, any authenticated user holding a user-mode auth URL could complete a flow bound to a different user, injecting their upstream OAuth tokens or header credentials under that user's identity. The canAccessUserFlow check mirrors the post-claim gate already present in CompleteUserOAuthFlow and closes the same class of vulnerability on the flow detail, start, and submit endpoints. Temp token minting is intentionally skipped for user-mode flows to prevent the middleware bypass that would nullify the gate.

Checklist

• I read docs/contributing/README.md and followed the guidelines
• I added/updated tests where appropriate
• I updated documentation where needed
• I verified builds succeed (Go and UI)
• I verified the CI pipeline passes locally if applicable

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[Pratham-Mishra04]

• fix: gate user-mode flows on caller user_id and skip temp token mint #3841 👈 (View in Graphite)
• refactor: rename staticHeadersResolver/serverOAuthResolver to sharedHeadersResolver/sharedOAuthResolver #3840
• refactor: remove deferred-fill user-mode OAuth flow support #3839
• dev

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[greptile-apps]

Confidence Score: 5/5

Safe to merge — the change is targeted security hardening with no functional regressions on existing non-user-mode paths.

All five changed surfaces consistently apply the identity gate. The temp-token skip is symmetric across both framework modules and correctly conditioned on MCPAuthModeUser only, leaving VK and session-mode behavior untouched. The UI goto redirect is encoded and validated against a /workspace allowlist before use.

No files require special attention.

Important Files Changed

Filename	Overview
transports/bifrost-http/handlers/mcp_sessions.go	Renames canReauthRow → canAccessUserFlow and expands the identity gate to flowDetail and flowStart; flowStart now correctly captures and gates on the loaded flow (previously discarded return value).
transports/bifrost-http/handlers/mcp_per_user_headers.go	Adds canAccessUserFlow identity gate to both flowDetail and flowSubmit for the per-user headers surface; gate placement is correct (after 404 guard, before processing).
framework/oauth2/main.go	Skips temp-token minting for user-mode OAuth flows to prevent the temp-token middleware branch from bypassing cookie resolution and nullifying the new identity gate.
framework/mcp_headers/main.go	Same temp-token minting skip applied to user-mode header-submission flows; symmetric with the OAuth change.
ui/lib/store/apis/baseApi.ts	401 redirect now preserves current path + query as an encoded goto parameter; normalizeLoginGoto validates the destination is a /workspace route before consuming it.

_{Reviews (2): Last reviewed commit: "feat: user bound to checks on mcp per us..." | Re-trigger Greptile}

[akshaydeo]

Merge activity

• May 28, 12:21 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• May 28, 12:24 PM UTC: @akshaydeo merged this pull request with Graphite.

The base branch was changed.