2026-09-08 · 6 min read · Rahul Chitturi
- authentication
- proxy
- debugging
An API can return 401 because a valid token never reaches its verifier. Browsers, redirects, CDNs, ingress controllers, service meshes, and application servers may omit, replace, reject, or route an Authorization header differently.
Decoding the token repeatedly will not diagnose a transport boundary. First prove which component received which safe metadata without copying the credential into logs or tickets.
Trace the request hop by hop
Record the original origin and URL, redirect chain, request method, authentication scheme, header presence, approximate size, route, and response challenge. Use booleans or a one-way diagnostic identifier rather than logging the token.
- Confirm the client sends Authorization on the failing request
- Check proxy allowlists and upstream header replacement rules
- Inspect redirects across origins, schemes, and ports
- Separate header rejection from signature and claim failures
Keep authentication ownership explicit
Document whether the edge authenticates and forwards verified identity, or whether the application receives and verifies the bearer token. Mixing both models can create duplicate checks or trust an unauthenticated identity header.
Return a useful WWW-Authenticate challenge without token contents. Apply header-size limits consistently, and do not fix forwarding by dumping all incoming headers into observability systems.
A Flashman workflow
Use the JWT tool only with synthetic tokens, URL tool for redirect and authority checks, diff for proxy configuration, timestamp converter for expiry evidence, and JSON formatter for redacted request metadata.
Test direct and proxied requests, same-origin and cross-origin redirects, oversized headers, duplicate Authorization fields, scheme casing, expired test tokens, and every production route.