Let's break down why your upstream service isn't receiving the expected headers when using OAuth2 Proxy. Here are the most common issues and how to fix them:

1. Verify OAuth2 Proxy Version Compatibility #

Not all parameters behave consistently across versions. For example, the --pass-authorization-header flag was stabilized in v7.0.0+, and older versions might have bugs or different naming conventions. Run this command to check your installed version:

oauth2-proxy --version

If you're on an older release, upgrading to the latest stable version often resolves header-related quirks.

2. Ensure Your Configuration Is Applied Correctly #

Double-check that your flags are properly included in the OAuth2 Proxy startup command, or if using a config file, that the corresponding settings are enabled:

• For command-line execution:

  oauth2-proxy --pass-authorization-header --pass-access-token [your other flags]
  

• For a config file (e.g., oauth2-proxy.cfg):

  pass_authorization_header = true
  pass_access_token = true
  

Typos or omitted flags are a common culprit—copy-paste these lines to avoid mistakes.

3. Check for Intermediate Proxies Filtering Headers #

If there's another reverse proxy (like Nginx, Apache, or Traefik) between OAuth2 Proxy and your upstream service, it might be stripping or modifying headers:

• Nginx: By default, Nginx drops headers with underscores (like X-Forwarded-Access-Token). Add underscores_in_headers on; to your server block to allow these headers to pass through.
• Other proxies: Look for settings that restrict request headers, and ensure they're configured to forward Authorization and X-Forwarded-Access-Token unmodified.

4. Confirm the User Is Fully Authenticated #

These headers are only added when a user has successfully completed the authorization code flow. If the user hasn't logged in yet, OAuth2 Proxy will redirect them to the identity provider instead of forwarding headers.

To confirm a valid session:

• Check OAuth2 Proxy's logs for lines like Authenticated user: [username]—this confirms the session is active.
• Test the flow by explicitly logging in, then making a request to your upstream service.

5. Enable Debug Logs to Inspect Forwarded Requests #

Turn on debug logging in OAuth2 Proxy to see exactly what headers are being sent to the upstream. Add --log-level debug to your startup command, then look for entries starting with UpstreamRequest. You should see lines like:

UpstreamRequest: GET /your-path HTTP/1.1, Headers: map[Authorization:[Bearer <your-token>] X-Forwarded-Access-Token:[your-token]]

If these headers aren't present in the debug logs, the issue lies with OAuth2 Proxy's configuration. If they are present, the problem is with your upstream service not reading them correctly.

6. Validate Upstream Service Header Handling #

Some backend frameworks or servers automatically normalize or filter headers:

• Ensure your upstream service is checking for the correct header names (headers are case-insensitive, but double-check for typos like Autorization instead of Authorization).
• If using a framework like Spring Boot, confirm that its security configuration isn't stripping the Authorization header by default.

内容的提问来源于stack exchange，提问作者Yannic Bürgmann