Fix refresh token bugs: preserve on OIDC omission, deduplicate concurrent refreshes

[bd73-com]

Summary

Fixes two bugs in the OIDC token refresh middleware (isAuthenticated) that caused intermittent session invalidation. The refresh token was silently overwritten with undefined when the OIDC provider omitted it from the response (violating RFC 6749 §6), and concurrent requests with expired tokens raced to call refreshTokenGrant, invalidating rotated tokens.

Closes #268, closes #269.

Changes

Refresh token preservation (bug #268)

• Use nullish coalescing (tokens.refresh_token ?? user.refresh_token) in updateUserSession to preserve the existing token when the OIDC provider omits it from the refresh response

Concurrent refresh deduplication (bug #269)

• Add per-session in-flight promise cache (inflightRefreshes Map) keyed by req.sessionID
• First request creates the refresh promise; concurrent requests for the same session await it
• Promise returns TokenResult so each waiter updates its own req.user object (Express deserializes separate user references per request)
• 15-second timeout via Promise.race prevents indefinite hangs from stalling OIDC providers
• Defensive cap at 10,000 entries with console.warn when reached — degrades gracefully by skipping dedup
• Cleanup via .catch(() => {}).finally(() => delete) prevents unhandled rejections and map leaks

Tests

• Test: refresh token preserved when OIDC omits it
• Test: concurrent refresh calls deduplicated (single refreshTokenGrant call)
• Test: both concurrent waiters receive fresh tokens
• Test: rejection propagates 401 to all concurrent waiters
• Added sessionID to mock request objects

How to test

1. npm run check && npm run test — all 1767 tests pass
2. npm run build — production build succeeds
3. Manual: Log in, wait for token expiry, trigger concurrent API calls — both should succeed without 401
4. Manual: Test with an OIDC provider that omits refresh_token in refresh responses — session should persist

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📒 Files selected for processing (2)

• server/replit_integrations/auth/replitAuth.test.ts
• server/replit_integrations/auth/replitAuth.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch claude/fix-bugs-dw5NV

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