401 Unauthorized vs 403 Forbidden

401 means authentication is missing or invalid. 403 means identity is known but lacks permission.

Aspect	401 Unauthorized	403 Forbidden
When it happens	Emitted when conditions specific to 401 unauthorized occur.	Emitted when conditions specific to 403 forbidden occur.
How to tell apart	Identify which layer emitted the code and inspect headers/logs for that layer.	Confirm whether problem is auth/policy, upstream quality, overload, or timeout.
Troubleshooting first step	Trace request ID through edge and application logs.	Check deploy/config changes and dependency health in same time window.
Practical note	Do not mask this response with generic handlers.	Return explicit headers like Retry-After or auth challenge when relevant.

When each appears in production

Use CDN/proxy logs to find emission point, then app logs/traces to isolate root cause.

Validate routing, policy, and timeout budgets in order. Fix the first failing layer before tuning client retries.