HTTP 401 Unauthorized vs 502 Bad Gateway
HTTP 401 (Unauthorized) is a 4xx Client Error response, while 502 (Bad Gateway) is a 5xx Server Error response. 401 indicates that the request requires user authentication. The response includes a WWW-Authenticate header indicating the authentication scheme. In contrast, 502 means that the server, acting as a gateway or proxy, received an invalid response from the upstream server.
Description
The request requires user authentication. The response includes a WWW-Authenticate header indicating the authentication scheme.
When You See It
When accessing a protected resource without credentials or with expired tokens.
How to Fix
Include valid authentication credentials (API key, Bearer token, Basic auth) in the Authorization header.
Description
The server, acting as a gateway or proxy, received an invalid response from the upstream server.
When You See It
When Nginx/Apache can't reach the application server (e.g., Gunicorn is down, upstream timeout).
How to Fix
Check if the upstream server is running. Verify proxy configuration. Check for upstream timeouts.
Key Differences
401 is a 4xx Client Error response, while 502 is a 5xx Server Error response.
HTTP 401: The request requires user authentication. The response includes a WWW-Authenticate header indicating the authentication scheme.
HTTP 502: The server, acting as a gateway or proxy, received an invalid response from the upstream server.
You encounter 401 when when accessing a protected resource without credentials or with expired tokens.
You encounter 502 when when Nginx/Apache can't reach the application server (e.g., Gunicorn is down, upstream timeout).
When to Use Which
For 401 (Unauthorized): Include valid authentication credentials (API key, Bearer token, Basic auth) in the Authorization header. For 502 (Bad Gateway): Check if the upstream server is running. Verify proxy configuration. Check for upstream timeouts.