Bug Description
When adding a custom remote MCP server to Claude.ai (via Settings → Connectors → Add custom connector) using a self-hosted Twenty CRM instance, the OAuth authentication flow fails with a "Connection was not possible" error. The browser briefly opens a popup attempting to redirect to claude.ai/desktop/... instead of completing the web OAuth callback, and the connector never authenticates successfully.
This occurs even though the same MCP server URL (streamable-http transport) works correctly in VS Code and Claude Desktop, where the Bearer token is handled directly without a browser OAuth flow.
Expected behavior
The OAuth flow should complete successfully in the browser, redirect to https://claude.ai/api/mcp/auth_callback, and allow the custom connector to authenticate and connect to the self-hosted Twenty MCP server.
Technical inputs
Twenty self-hosted instance running v1.23.4
MCP server configured with streamable-http transport at a public HTTPS endpoint
The MCP server is reachable over the public internet (confirmed via external HTTP requests)
Twenty's MCP OAuth appears designed for local clients (VS Code, Cursor, Windsurf) that handle Bearer tokens directly — it does not implement the server-side OAuth callback flow required by Claude.ai (https://claude.ai/api/mcp/auth_callback)
VS Code connects successfully using the same URL because it handles the token locally without a browser redirect
Workaround: connecting via a direct Bearer token using the ?token= query param works, but is not ideal for production use
Bug Description
When adding a custom remote MCP server to Claude.ai (via Settings → Connectors → Add custom connector) using a self-hosted Twenty CRM instance, the OAuth authentication flow fails with a "Connection was not possible" error. The browser briefly opens a popup attempting to redirect to claude.ai/desktop/... instead of completing the web OAuth callback, and the connector never authenticates successfully.
This occurs even though the same MCP server URL (streamable-http transport) works correctly in VS Code and Claude Desktop, where the Bearer token is handled directly without a browser OAuth flow.
Expected behavior
The OAuth flow should complete successfully in the browser, redirect to https://claude.ai/api/mcp/auth_callback, and allow the custom connector to authenticate and connect to the self-hosted Twenty MCP server.
Technical inputs
Twenty self-hosted instance running v1.23.4
MCP server configured with streamable-http transport at a public HTTPS endpoint
The MCP server is reachable over the public internet (confirmed via external HTTP requests)
Twenty's MCP OAuth appears designed for local clients (VS Code, Cursor, Windsurf) that handle Bearer tokens directly — it does not implement the server-side OAuth callback flow required by Claude.ai (https://claude.ai/api/mcp/auth_callback)
VS Code connects successfully using the same URL because it handles the token locally without a browser redirect
Workaround: connecting via a direct Bearer token using the ?token= query param works, but is not ideal for production use