MCP OAuth login cannot pass RFC 8707 resource parameter

Summary

OAuth login for MCP servers does not provide a way to include the RFC 8707 resource parameter in the authorization request. Some OAuth providers require resource, so the login flow fails even though the user completes authorization in the browser.

Repro

1. Configure a streamable HTTP MCP server that uses OAuth and requires resource on the authorization request.
2. Run codex mcp login <server-name>.
3. The browser flow completes, but the token exchange fails (no access_token), because the authorization URL never included resource.

Expected

Codex should allow specifying an OAuth resource value per MCP server and append it to the authorization URL when starting the login flow.

Notes

The current flow only passes scope, redirect_uri, and client_name. There is no config/CLI way to pass an OAuth resource value.