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fix(mcp): advertise the authorization server verbatim in protected-resource metadata - #50
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…source metadata The SDK's ProtectedResourceMetadata types authorization_servers as AnyHttpUrl, and pydantic renders the bare origin as "https://zernio.com/". MCP SDK 2.x clients (Hermes Agent 0.21+) compare that byte for byte with the issuer "https://zernio.com" from zernio.com/.well-known/oauth-authorization-server (SEP-2468) and abort with "Authorization server metadata issuer mismatch". Axiom shows 12 Hermes 0.21.5 IPs looping on the issuer document in the last 48h and zero registrations from that user agent. Upstream fixed the model in mcp 2.0 (url_preserve_empty_path), which fastmcp 3.x cannot resolve to, so the document is rendered by a RemoteAuthProvider subclass instead. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_011CMTnkAaNe8GJksNdAwg3K
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Why
Every new Hermes Agent 0.21.x connection to
mcp.zernio.comfails withAuthorization server metadata issuer mismatch: https://zernio.com != https://zernio.com/. The SDK'sProtectedResourceMetadatatypesauthorization_serversasAnyHttpUrl, pydantic renders the bare origin with a trailing slash, and MCP SDK 2.x clients compare it byte for byte with the issuer fromzernio.com/.well-known/oauth-authorization-server(SEP-2468). Axiom shows 12 Hermes 0.21.5 IPs looping on the issuer document in the last 48h and zero registrations from that user agent. Existing installs are unaffected (a stored refresh token skips discovery).What
VerbatimIssuerRemoteAuthProviderrenders the RFC 9728 document itself withauthorization_serversas the configured strings; route path, CORS, cache header, scopes narrowing (ChatGPT surface) and resource are unchanged.Upstream fixed the model in mcp 2.0 (
url_preserve_empty_path), but fastmcp 3.x caps mcp at 1.30.0, which still lacks it. Same change landed in the dormantzernio-mcprepo as #2 before I noticeddevelophere is what Railway serves.🤖 Generated with Claude Code
https://claude.ai/code/session_011CMTnkAaNe8GJksNdAwg3K