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Your team configures CORSMiddleware with a wildcard for allow_origins and also turns on allow_credentials for cookie based logins. What actually happens to a real cross origin request?
allow_origins
allow_credentials
It swaps out the wildcard and echoes back the exact origin that sent the request instead.
FastAPI refuses to start when both settings are combined.
It keeps sending the literal wildcard as the Access-Control-Allow-Origin header regardless, and browsers simply ignore the credentials setting in that case.