Hugging Face MCP authentication: known deviations
Opaque tokens with scopes sometimes only visible on a second, non-OIDC endpoint — plus hardcoded fallbacks.
How Hugging Face deviates from the MCP authorization spec
- Opaque tokens; granted scopes sometimes appear only under a nested shape on a second non-OIDC endpoint.
- Common integrations fall back to hardcoded scopes when the real ones cannot be read.
How to spot it without credentials
Authorize at huggingface.co/oauth/authorize.
What it breaks in production
The same fabricated-scope class as GitHub: what a server believes was granted and what actually was granted diverge silently.
Check a Hugging Face-backed MCP server
The free scanner runs the discovery and client-compatibility checks with no credentials, and every finding cites the spec requirement it violates:
npx mcpcomp https://your-mcp-server.example/mcp