Discovery metadata was merged without the https/loopback endpoint rule that
configured endpoints already pass, letting a malicious issuer downgrade the
authorization/token/device/registration endpoint after config validation.
- Add exported ValidateEndpointURL as the single endpoint-safety rule;
validateTokenEndpoint now delegates to it.
- Backstop in BuildAuthorizationURL (the choke point both the provider and MCP
flows build their browser URL through).
- Validate each discovered endpoint before merge in the provider resolveEndpoints
and validate resolved MCP metadata in both branches; fail closed on insecure.
Co-authored-by: KRATOS <[email protected]>