Problem

The mcp-remote npm package was failing to connect to the MCP server with the error:
Fatal error: Error: Cannot find localhost callback URI from existing client information

The issue was that the OAuth authorization server metadata endpoint (/.well-known/oauth-authorization-server) was not advertising supported redirect URIs, which mcp-remote requires
to discover valid callback URLs for the OAuth flow.

Root Cause

The HandleAuthorizationServerMetadata function in internal/oauth/metadata.go was missing the redirect_uris field in the OAuth 2.0 Authorization Server Metadata response (RFC 8414).
This prevented OAuth clients like mcp-remote from discovering which callback URIs are supported for the authorization code flow.

Solution

Added redirect_uris field to the OAuth authorization server metadata response when OAUTH_REDIRECT_URI is configured:

// Add redirect URIs for mcp-remote compatibility
if h.config.RedirectURI != "" {
metadata["redirect_uris"] = []string{h.config.RedirectURI}
}

Configuration

For this fix to work, the server must be deployed with:
export OAUTH_REDIRECT_URI="https:///oauth/callback"

Testing

After deployment with the environment variable set, verify the fix works:
curl https:///.well-known/oauth-authorization-server

Should now include:
{
"redirect_uris": ["https:///oauth/callback"],
...
}

Impact

• ✅ Enables mcp-remote to successfully discover callback URIs
• ✅ Maintains backward compatibility (no redirect_uris if not configured)
• ✅ Follows OAuth 2.0 RFC 8414 specification
• ✅ No breaking changes to existing functionality

This allows clients using mcp-remote to successfully complete the OAuth authorization flow with the MCP server.