- Kube-apiserver: Made sure that when `--requestheader-client-ca-file` and `--client-ca-file` contain overlapping certificates, `--requestheader-allowed-names` must be specified so that regular client certificates cannot set authenticating proxy headers for arbitrary users. ([#131411](https://github.com/kubernetes/kubernetes/pull/131411), [@ballista01](https://github.com/ballista01)) [SIG API Machinery, Auth and Security]

For more information, see [#53288](https://issue.k8s.io/53288).

- Added `apiserver.latency.k8s.io/authentication` annotation to the audit log to record the
  time spent authenticating slow requests. Also added `apiserver.latency.k8s.io/authorization`

- kube-apiserver: a new `--requestheader-uid-headers` flag allows configuring request header authentication to obtain the authenticating user's UID from the specified headers. The suggested value for the new option is `X-Remote-Uid`. When specified, the `kube-system/extension-apiserver-authentication` configmap will include the value in its `.data[requestheader-uid-headers]` field....