OAuth flow hangs indefinitely when server rejects dynamic client registration (e.g., Figma MCP)

[leandroppf]

When running mcporter auth 'https://mcp.figma.com/mcp', the CLI prints "Waiting for browser approval..." and hangs until timeout, but the browser never opens. No error is surfaced at any log level,
including --log-level debug.

Steps to Reproduce

1. Configure Figma MCP server: "figma-remote-mcp": { "type": "http", "url": "https://mcp.figma.com/mcp" }
2. Run mcporter auth 'https://mcp.figma.com/mcp' --log-level debug
3. Observe: CLI prints "Waiting for browser approval..." but browser never opens
4. Wait 60s → times out with OAuthTimeoutError

Root Cause

Figma's OAuth server does not support RFC 7591 Dynamic Client Registration (https://datatracker.ietf.org/doc/html/rfc7591). When mcporter attempts to register itself as an OAuth client, Figma
responds with HTTP 403 Forbidden (raw body: "Forbidden").

Because client registration fails, no authorization URL is ever generated, so redirectToAuthorization() is never called and the browser never opens.

The error is caught inside the MCP SDK's auth() → authInternal() flow and never surfaces to the user. The actual error is:

  HTTP 403: Invalid OAuth error response: SyntaxError: Unexpected token 'F', "Forbidden" is not valid JSON. Raw body: Forbidden                                                                        

This same server works fine in Claude CLI, which has a pre-registered OAuth client ID and doesn't need dynamic client registration.

Expected Behavior

1. Surface the error — mcporter should log the 403 rejection with a clear message like: "OAuth client registration was rejected by the server (HTTP 403). This server may not support dynamic client
   registration."
2. Don't hang — if the authorization URL was never generated, mcporter should fail immediately instead of waiting 60s for a browser callback that will never come
3. Ideally — support providing a pre-registered client_id / client_secret via config or CLI flags for servers that don't allow dynamic registration

Environment

• mcporter: 0.7.3
• Node: v22.18.0
• macOS
• MCP SDK: @modelcontextprotocol/sdk (bundled with mcporter)

Affected servers

• https://mcp.figma.com/mcp — confirmed
• Likely any MCP server that requires pre-registered OAuth clients