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Banner: Google sign-in failing with Error 400 redirect_uri_mismatch behind a TLS proxy

Web Development Bug Report

Google sign-in fails with Error 400: redirect_uri_mismatch only in production

Daniel Tran · Aug 21, 2025 · 9 min read

Sign in with Google worked locally and on staging but failed in production with redirect_uri_mismatch. Behind the TLS proxy our FastAPI app built an http:// callback because Uvicorn did not trust the proxy's headers. How we traced and fixed it.

Banner: a single-lane road with one stalled truck holding up every other request behind it

Programming Languages Bug Report

FastAPI freezes all requests: a blocking call inside async def stalls the event loop

Daniel Tran · Jul 22, 2025 · 9 min read

One slow partner API call made our whole FastAPI service stop answering, health checks included, until Kubernetes restarted the pods. A synchronous requests call and a time.sleep inside async def were blocking the event loop.