Serve OAuth protected resource metadata (RFC 9728) on the MCP server#48
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The bearer-auth middleware already advertises a resource_metadata URL in 401 WWW-Authenticate headers, but no route served it, so spec-compliant clients following the pointer got a 404 (modelcontextprotocol#22). In EXTERNAL mode there was no way to discover the authorization server at all besides the legacy RFC 8414 shim. - Serve RFC 9728 protected resource metadata at /.well-known/oauth-protected-resource (the URL advertised in 401s) and /.well-known/oauth-protected-resource/mcp (RFC 9728 path insertion), listing the mode-appropriate authorization server - Keep the legacy /.well-known/oauth-authorization-server shim for clients of the 2025-03-26 spec revision, and label it as such Fixes modelcontextprotocol#22 Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Fixes #22.
The MCP module's
requireBearerAuthalready advertises aresource_metadataURL in 401WWW-Authenticateheaders (viagetOAuthProtectedResourceMetadataUrl), but nothing ever served that path — so clients that follow the spec's discovery flow got a 404. In EXTERNAL mode this made authorization-server discovery effectively impossible except through the legacy shim.Changes (in
src/index.ts, mirroring the existing inline metadata shim style):/.well-known/oauth-protected-resource(the exact URL advertised in 401s) and/.well-known/oauth-protected-resource/mcp(RFC 9728 §3.1 path insertion, for clients that derive the metadata URL from the/mcpendpoint themselves).authorization_serverspoints at the in-process server in INTERNAL mode and atAUTH_SERVER_URLin EXTERNAL mode./.well-known/oauth-authorization-servershim rather than removing it as the issue suggests: clients of the 2025-03-26 spec revision discover auth by querying that path on the MCP server directly, and in EXTERNAL mode the shim correctly points them at the external AS endpoints. It's now commented as a back-compat shim; happy to remove it instead if you'd prefer strict current-spec behavior.Verified by booting both modes and curling:
AUTH_MODE=external AUTH_SERVER_URL=http://localhost:3001): both PRM endpoints returnauthorization_servers: ["http://localhost:3001"], and the URL in the 401'sWWW-Authenticate: ... resource_metadata="…"now resolves.npm run build,npx eslint, and the jest suite (79 tests, 6 suites) all pass.🤖 Generated with Claude Code