### PodSecurity graduates to Beta

[PodSecurity](https://kubernetes.io/docs/concepts/security/pod-security-admission/) moves to Beta.
`PodSecurity` replaces the deprecated `PodSecurityPolicy` admission controller.

- Added a new Prometheus counter metric `sync_proxy_rules_iptables_restore_failures_total` for kube-proxy iptables-restore failures (both ipvs and iptables modes)
  ([#81210](https://github.com/kubernetes/kubernetes/pull/81210), [@figo](https://github.com/figo))

- `kubectl create token` can now be used to request a service account token, and permission to request service account tokens is added to the `edit` and `admin` RBAC roles ([#107880](https://github.com/kubernetes/kubernetes/pull/107880), [@liggitt](https://github.com/liggitt))

* Kubernetes now supports up to 5,000 nodes via etcd v3, which is enabled by default.
* [Role-based access control (RBAC)](https://kubernetes.io//docs/admin/authorization/rbac) has graduated to beta, and defines secure default roles for control plane, node, and controller components.
* The [`kubeadm` cluster bootstrap tool](https://kubernetes.io/docs/getting-started-guides/kubeadm/) has graduated to beta. Some highlights:

- kube-proxy no longer automatically cleans up network rules created by running kube-proxy in other modes. If you are switching the kube-proxy mode (EG: iptables to IPVS), you will need to run `kube-proxy --cleanup`, or restart the worker node (recommended) before restarting kube-proxy. If you are not switching kube-proxy between different modes, this change should not require any action. ([#76109](https://github.com/kubernetes/kubernetes/pull/76109), [@vllry](https://github.com/vllry))...

* Fix credentials providers for docker sandbox image. ([#51870](https://github.com/kubernetes/kubernetes/pull/51870), [@feiskyer](https://github.com/feiskyer))
* Fix security holes in GCE metadata proxy. ([#51302](https://github.com/kubernetes/kubernetes/pull/51302), [@ihmccreery](https://github.com/ihmccreery))

    * If you are not switching kube-proxy between different modes, this change should not require any action.

`kube-apiserver`: added `--authorization-config` flag for reading a configuration file containing an `apiserver.config.k8s.io/v1alpha1 AuthorizationConfiguration` object. The `--authorization-config` flag is mutually exclusive with `--authorization-modes` and `--authorization-webhook-*` flags. The `alpha` `StructuredAuthorizationConfiguration` feature flag must be enabled for `--authorization-config` to be specified. ([#120154](https://github.com/kubernetes/kubernetes/pull/120154), [@palnabarun](h...