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4xx Client & Proxy Request

HTTP 401 Unauthorized — Reverse Proxy & Gateway Troubleshooting

HTTP 401 Unauthorized signals that the request lacks valid authentication credentials for the target resource, or that an OAuth2/OIDC bearer JWT has expired, failed signature validation, or mismatched its expected audience (aud) claim.

Status Code401 Unauthorized
Specification / OriginRFC 9110 §15.5.2
Failure LayerAPI Gateway / Auth Middleware
Retry SafetyDo not blind-retry without fixing request syntax, auth, or origin certificate

Interactive HTTP 401 Live Probe & Log Command Builder

Enter your target endpoint below to generate copy-ready curl latency breakdown probes and origin bypass tests:


  

    Related diagnostics:
    Nginx & Caddy Proxy Generator → ·
    X.509 SSL Certificate Decoder → ·
    Offline JWT Expiry Inspector →
  






  
Production Root Causes & Remediation Guide

  
Common triggers include clock skew between token issuers and API gateways invalidating nbf or exp timestamps, missing Authorization: Bearer prefixes, rotated JWKS signing keys (kid mismatch), or reverse proxies stripping Authorization headers across redirects.

  
Step-by-Step Engineering Fix

  
Decode the bearer token locally to inspect exp, iat, iss, and aud claims, synchronize NTP chrony daemons across gateway nodes, and ensure proxy_set_header Authorization $http_authorization is preserved when proxying upstream.

  
Recommended Nginx / Reverse-Proxy Configuration Snippet

  
proxy_set_header Authorization $http_authorization;
proxy_pass_header WWW-Authenticate;







  
Frequently Asked Questions (HTTP 401)

  
  

    What is the difference between HTTP 401 Unauthorized and 403 Forbidden?
    
HTTP 401 means authentication is missing or invalid (who are you?), whereas HTTP 403 means your identity is known or irrelevant, and policy explicitly denies access (you lack permission).

  

  
  

    Which infrastructure layer generates HTTP 401 Unauthorized?
    
HTTP 401 (RFC 9110 §15.5.2) typically originates at the API Gateway / Auth Middleware layer. HTTP 401 Unauthorized signals that the request lacks valid authentication credentials for the target resource, or that an OAuth2/OIDC bearer JWT has expired, failed signature validation, or mismatched its expected audience (aud) claim.

  

  
  

    Should API clients automatically retry HTTP 401 responses?
    
Do not blind-retry HTTP 401 without fixing the underlying request payload, authentication token, or origin TLS certificate first.

  

  






  
Browse All 25 Gateway, Proxy & Cloud HTTP Error Guides

  

    
      HTTP 400 (Bad Request)
    
      HTTP 401 (Unauthorized)
    
      HTTP 403 (Forbidden)
    
      HTTP 404 (Not Found)
    
      HTTP 405 (Method Not Allowed)
    
      HTTP 408 (Request Timeout)
    
      HTTP 413 (Content Too Large)
    
      HTTP 422 (Unprocessable Content)
    
      HTTP 429 (Too Many Requests)
    
      HTTP 431 (Request Header Fields Too Large)
    
      HTTP 499 (Client Closed Request)
    
      HTTP 500 (Internal Server Error)
    
      HTTP 501 (Not Implemented)
    
      HTTP 502 (Bad Gateway)
    
      HTTP 503 (Service Unavailable)
    
      HTTP 504 (Gateway Timeout)
    
      HTTP 507 (Insufficient Storage)
    
      HTTP 511 (Network Authentication Required)
    
      HTTP 520 (Web Server Returned an Unknown Error)
    
      HTTP 521 (Web Server Is Down)
    
      HTTP 522 (Connection Timed Out)
    
      HTTP 523 (Origin Is Unreachable)
    
      HTTP 524 (A Timeout Occurred)
    
      HTTP 525 (SSL Handshake Failed)
    
      HTTP 526 (Invalid SSL Certificate)
    
  






  


  
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