According to the spec,

The specific use of authorization_servers is beyond the scope of this specification; implementers should consult OAuth 2.0 Protected Resource Metadata (RFC9728) for guidance on implementation details.

https://modelcontextprotocol.io/specification/2025-06-18/basic/authorization

In the SDK I checked, only the first authorization server is used:

https://github.com/modelcontextprotocol/typescript-sdk/blob/4d0977bc9169965233120e823c8024e210132ad9/src/client/auth.ts#L328

https://github.com/modelcontextprotocol/python-sdk/blob/c7671e470c235971b63c41be183537074ff8fa91/src/mcp/client/auth.py#L250

Are they by design?