CVE-2026-116672: Authlib RFC 7592 examples omit registration-access-token client binding

RFC 7592 (OAuth 2.0 Dynamic Client Registration Management Protocol) lets a previously registered client read, update, or delete its own registration, authenticated by a registration_access_token issued specifically to that client at registration time. The entire security model of this protocol depends on the server verifying that the token presented in the request actually belongs to the client identified in the request, not merely that the token is valid for some client.

Authlib’s ClientConfigurationEndpoint implements the control flow correctly in structure, calling authenticate_token, then authenticate_client, then check_permission, and treats all three as abstract methods that “Developers MUST implement in subclass.” The problem is that the documented example implementations for these methods, taken together exactly as written, never perform the one check that matters: binding the authenticated token to the specific client being accessed. A developer who implements these methods by following the provided examples ends up with a complete authorization bypass on this endpoint.