Add readiness check for metrics server when using `WithAuthenticationAndAuthorization()

We’ve observed that when using WithAuthenticationAndAuthorization() (with self-signed certs), the metrics server may take a few seconds to become available on Kubernetes 1.33+.

In particular, some Kubebuilder tests started failing against 1.33, where they were still passing in previous versions < 1.33. After debugging, the root cause seems to be a delay related to how Kubernetes 1.33 handles token availability and cert readiness, likely due to changes in the API server behaviour.

To solve our tests for 1.33+ we added a delay: https://github.com/kubernetes-sigs/kubebuilder/pull/4882/files

Just an Idea

It might be nice if controller-runtime could provide a ReadyzCheck for the metrics server. That would help in scenarios using either self-signed or provided certs, by allowing consumers to verify the /metrics endpoint is actually ready (serving over HTTPS and accepting tokens) before probing or testing.

Thanks for your work and for considering this 🙌

Start by reviewing the metrics server path used with WithAuthenticationAndAuthorization() and the existing /metrics endpoint behavior. Compare the readiness expectations with the linked Kubebuilder change for Kubernetes 1.33. Done means consumers can check that the HTTPS metrics endpoint is serving and accepting tokens before probing or testing it.