HTTP 401 Unauthorized vs 431 Request Header Fields Too Large
Both HTTP 401 (Unauthorized) and 431 (Request Header Fields Too Large) belong to the 4xx Client Error category. 401 indicates that the request requires user authentication. The response includes a WWW-Authenticate header indicating the authentication scheme. Meanwhile, 431 means that the server refuses to process the request because an individual header field or all headers collectively are too large.
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 refuses to process the request because an individual header field or all headers collectively are too large.
When You See It
When cookies accumulate to an excessive size, or a single header (like Authorization) is too long.
How to Fix
Reduce header sizes. Clear excessive cookies. Use shorter tokens.
Key Differences
HTTP 401: The request requires user authentication. The response includes a WWW-Authenticate header indicating the authentication scheme.
HTTP 431: The server refuses to process the request because an individual header field or all headers collectively are too large.
You encounter 401 when when accessing a protected resource without credentials or with expired tokens.
You encounter 431 when when cookies accumulate to an excessive size, or a single header (like Authorization) is too long.
When to Use Which
For 401 (Unauthorized): Include valid authentication credentials (API key, Bearer token, Basic auth) in the Authorization header. For 431 (Request Header Fields Too Large): Reduce header sizes. Clear excessive cookies. Use shorter tokens.