The MCP authentication flow now supports custom redirectUri parameters and provides better error messages for invalid callback URLs: "Invalid callback URL — no authorization code. The flow is still open; retry with the full redirect URL."
Evidence
OAuth improvements (search for "Invalid callback URL", "No OAuth flow in progress")
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
How sure we are
One source agreesOne thing we can check says the same as this entry.
Anthropic's release notes agreeSDK: mcp_authenticate now supports redirectUri for custom scheme completion and claude.ai connectors
