Summary

gbrain auth register-client previously hard-coded redirect_uris = [] and token_endpoint_auth_method = NULL, which made the CLI unusable for the case SECURITY.md itself recommends it for — pre-registering Claude.ai / ChatGPT custom connectors so operators can run with --enable-dcr off.

New flags:

• --redirect-uri <uri> (repeatable; required for authorization_code clients)
• --token-endpoint-auth-method <method> (client_secret_post | none; ChatGPT custom connectors use none)

Auth-method values are validated against a new ALLOWED_TOKEN_ENDPOINT_AUTH_METHODS set that mirrors what the MCP SDK's mcpAuthRouter advertises in token_endpoint_auth_methods_supported. Unknown values fail loud at registration.

The failure mode this fixes

Before this PR, the SECURITY.md-recommended hardening path falls apart at step 2:

1. Operator drops --enable-dcr, runs gbrain auth register-client claude-ai --grant-types authorization_code,refresh_token --scopes "read write".
2. Pastes the client_id/secret into Claude.ai → /authorize returns {\"error\":\"invalid_request\",\"error_description\":\"Unregistered redirect_uri\"}.
3. Operator UPDATEs oauth_clients by hand to add the callback URLs, and again for token_endpoint_auth_method = 'none' to make ChatGPT's PKCE-only flow work.

Worked example after this PR

```bash
gbrain auth register-client claude-ai \
--grant-types authorization_code,refresh_token \
--scopes "read write" \
--redirect-uri https://claude.ai/api/mcp/auth_callback \
--redirect-uri https://claude.com/api/mcp/auth_callback

gbrain auth register-client chatgpt \
--grant-types authorization_code,refresh_token \
--scopes "read write" \
--redirect-uri https://chatgpt.com/connector/oauth/ \
--token-endpoint-auth-method none
```

Test plan

• `bun test test/oauth.test.ts` — 68 pass (4 new: redirect_uris persistence, `none` persistence, default `client_secret_post` fallback, unsupported-method rejection)
• Tested live against `https://brain.pdzeng.com\` (DCR disabled) with both Claude.ai and ChatGPT custom-connector flows — both reach `/authorize`, complete consent, and get `read,write` tokens.

Notes

• No DB schema change. `oauth_clients.token_endpoint_auth_method TEXT` already exists; the INSERT now sets it instead of leaving it NULL.
• Backward compatible: omitting both new flags reproduces today's behavior, except `token_endpoint_auth_method` defaults to `'client_secret_post'` explicitly instead of NULL — matching the DCR path (`oauth-provider.ts` line ~184).
• The CLI usage block + the typed signature on `registerClientManual` both expose the new fields.

🤖 Generated with Claude Code

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