* request a client certificate from the API server during the boot cycle and pause
    * waiting for the request to be satisfied. It will continually refresh the certificate
    * as the certificates expiration approaches.

- Kubeadm: allow the "certs check-expiration" command to not require the existence of the cluster CA key (ca.key file) when checking the expiration of managed certificates in kubeconfig files. ([#106930](https://github.com/kubernetes/kubernetes/pull/106930), [@neolit123](https://github.com/neolit123)) [SIG Cluster Lifecycle]

  * All communication is now over TLS
  * Authorization plugins can be installed by kubeadm, including the new default of RBAC
  * The bootstrap token system now allows token management and expiration
* The [`kubefed` federation bootstrap tool](https://kubernetes.io/docs/tutorials/federation/set-up-cluster-federation-kubefed/) has also graduated to beta.

* PodSecurityPolicy admission information has been added to audit logs. ([#58143](https://github.com/kubernetes/kubernetes/pull/58143), [@CaoShuFeng](https://github.com/CaoShuFeng))
* TokenRequests now are required to have an expiration duration between 10 minutes and 2^32 seconds. ([#63999](https://github.com/kubernetes/kubernetes/pull/63999), [@mikedanese](https://github.com/mikedanese))

- Kubelets configured to rotate client certificates now publish a `certificate_manager_server_ttl_seconds` gauge metric indicating the remaining seconds until certificate expiration. ([#91148](https://github.com/kubernetes/kubernetes/pull/91148), [@liggitt](https://github.com/liggitt)) [SIG Auth and Node]

  * Renamed Kubelet metric certificate_manager_server_expiration_seconds to certificate_manager_server_ttl_seconds and changed to report the second until expiration at read time rather than absolute time of expiry. 
  * Improved accuracy of Kubelet metric rest_client_exec_plugin_ttl_seconds.

  be removed in a future release) and added a new flag ''--output" that serves the
  same purpose. Affected commands are - "kubeadm config images list", "kubeadm token
  list", "kubeadm upgrade plan", "kubeadm certs check-expiration".' ([#124393](https://github.com/kubernetes/kubernetes/pull/124393), [@carlory](https://github.com/carlory)) [SIG Cluster Lifecycle]
- ACTION REQUIRED for custom scheduler plugin developers:

- The commands `kubeadm certs renew` and `kubeadm certs check-expiration` now honor the `cert-dir` flag on a running Kubernetes cluster. ([#110709](https://github.com/kubernetes/kubernetes/pull/110709), [@chendave](https://github.com/chendave))

- Kubeadm: fix panic in the command "kubeadm certs check-expiration" when "/etc/kubernetes/pki" exists but cannot be read. ([#124124](https://github.com/kubernetes/kubernetes/pull/124124), [@carlory](https://github.com/carlory)) [SIG Cluster Lifecycle]

* Improve explanation of ReplicaSet ([#53403](https://github.com/kubernetes/kubernetes/pull/53403), [@rcorre](https://github.com/rcorre))
* avoid newline "