401 Is Not the Bug. It’s the Signal.

You fixed the endpoint. You rewrote the dependency. You regenerated the token. Still 401. Here’s the uncomfortable truth: 401 is not the root cause. It’s the signal that something deeper is inconsistent. In FastAPI authentication flows, 401 usually appears when: The SECRET_KEY used to sign the token is not the one used to verify it Docker injects a different .env than your local environment Multiple instances are running with inconsistent configurations The token algorithm (HS256 / RS256) does not match Clock drift invalidates the token timestamp The controller is fine. The route is fine. The dependency is fine. The layers are not aligned. Authentication is not just code. It’s configuration. It’s environment. It’s deployment consistency. When /token works but /me returns 401, your application is telling you: “The layers don’t agree.” Stop fixing the endpoint. Start mapping the layers: Environment variables Key consistency Container configuration Token structure Deployment topology 401