Support a static callback URI for MCP authentication

Question

### What feature would you like to see?

From what I can tell the callback URI expected by codex is dynamically generated when doing MCP authentication. Specifically the port part of the localhost is randomly assigned. That is a bit of a problem because many authorizations servers require a static redirect URI. would it be possible for you to support a static callback URI. Something similar to what librechat or cline have.

### Additional information
Proposed solution is here: https://github.com