ErrorFindly
4014xx Client ErrorHigh

HTTP 401 Unauthorized

Defined in RFC 7235

What Does HTTP 401 Mean?

The request requires user authentication. The client must authenticate itself to get the requested response.

Common Causes

  1. 1Missing or expired authentication token
  2. 2Invalid API key or credentials
  3. 3Session timeout requiring re-login
  4. 4Missing Authorization header

Impact

  • ⚠Redirected to login page
  • ⚠API request rejected — must provide credentials
  • ⚠Logged out unexpectedly

Developer Fix

For web developers and application engineers

  1. 1Include proper Authorization header in requests
  2. 2Implement token refresh logic for expired tokens
  3. 3Handle 401 by redirecting to login flow
  4. 4Check that WWW-Authenticate header is returned

Server Admin Fix

For system administrators and DevOps engineers

  1. 1Verify authentication middleware is configured correctly
  2. 2Check token validation logic and expiration settings
  3. 3Review auth server availability and performance

Frequently Asked Questions

What's the difference between 401 and 403?
401 means 'not authenticated' — the server doesn't know who you are. 403 means 'not authorized' — the server knows who you are but you don't have permission. Despite the name 'Unauthorized', 401 is about authentication.
How do I fix a 401 error?
Log in again, provide valid API credentials, check if your token has expired, or ensure the Authorization header is included in your request.

Related HTTP Status Codes

403Forbidden407Proxy Authentication Required

About the Author

Web Infrastructure Team

Verified against official RFC specifications and real-world server configurations. HTTP status code behavior confirmed across Apache, Nginx, and Cloudflare.