"does not support dynamic client registration": pre-register an OAuth client and pass --client-id

Symptom

claude mcp login dcr fails with SDK auth failed: Incompatible auth server: does not support dynamic client registration.

Environment and tested versions

Debian GNU/Linux 13 (trixie) x86_64, node 20.19.2, npm 11.21.1; mock OAuth authorization server with no registration_endpoint (127.0.0.1); pseudo-terminal via script because mcp login needs a TTY; browser step completed with curl

• @anthropic-ai/claude-code 2.1.316
• node 20.19.2

Client used in the test: Tested against a local mock MCP server on 127.0.0.1, not a real provider. Client was Claude Code 2.1.316 itself.

Root cause

The authorization server doesn't offer dynamic client registration, so the client needs a client_id registered in advance.

Fix steps

1. Register an OAuth app with the provider, with redirect URI http://localhost:<port>/callback.
2. Run claude mcp add --transport http --client-id <id> --callback-port <port> <name> <url> (add --client-secret for confidential clients).
3. Run claude mcp login <name> and complete the browser sign-in.

Verification

Tested 31 Oct 2026 in a throwaway directory on a Linux box (fake credentials only). Before (A) and after the fix:

A: SDK auth failed: Incompatible auth server: does not support dynamic client registration
B: (after add --client-id test-client --callback-port 41957)
   authorize URL printed with client_id=test-client ... redirect_uri=http://localhost:41957/callback
   Authenticated with "dcr". Its tools are now available in Claude Code.
   claude mcp get dcr -> Status: ✔ Connected

Sources

• https://code.claude.com/docs/en/mcp (pre-configured OAuth credentials, --callback-port)