MCP OAuth token exchange fails in ChatGPT App, works in MCP Inspector

ChatGPT Apps SDK
, ,
1

I’m building an MCP server with OAuth (auth code flow).

  • The auth flow works in MCP Inspector

  • The same server fails at the token exchange step when creating a ChatGPT App

This suggests a difference in the token request parameters (e.g. redirect_uri, PKCE, or client auth method).

Has anyone documented the exact OAuth token exchange requirements used by ChatGPT for MCP Apps, or seen differences vs MCP Inspector?

I can share redacted token endpoint logs if helpful. Please see the attached screenshot for better understanding.

token-exchange-issue
token-exchange-issue2014×903 82.4 KB

2

….update people..

I have debugged through this issue, and found that ChatGPT sends the Basic Authorization header for this token exchange call: POST /oauth/token. See the screenshot below. Is that a standard prescribed way by OAuth2.1?

3

I resolved it by adding extra check for the Basic Auth header for the /token exchange call. Its working now.