- Kube-apiserver can now specify `--authentication-token-webhook-version=v1` or `--authorization-webhook-version=v1` to use `v1` TokenReview and SubjectAccessReview API objects when communicating with authentication and authorization webhooks. ([#84768](https://github.com/kubernetes/kubernetes/pull/84768), [@liggitt](https://github.com/liggitt))

- Fix bug to prevent allocation of existing floating IP.
- Fix Cinder authentication bug when OS_DOMAIN_NAME not specified.
- Fix Keystone authentication errors by skipping synchronization for unscoped tokens.
- Fix authentication error for client-auth-plugin
- Fix dependency references from in-tree-provider to point to external provider.
- Add shutdown instance by Provider ID.

* API server authentication now caches successful bearer token authentication results for a few seconds. ([#50258](https://github.com/kubernetes/kubernetes/pull/50258), [@liggitt](https://github.com/liggitt))

- Kubectl azure authentication: fixed a regression in 1.18.0 where "spn:" prefix was unexpectedly added to the `apiserver-id` configuration in the kubeconfig file ([#89706](https://github.com/kubernetes/kubernetes/pull/89706), [@weinong](https://github.com/weinong)) [SIG API...

  or the `KUBE-MARK-MASQ` chain (which is now only created by kube-proxy). ([#119374](https://github.com/kubernetes/kubernetes/pull/119374), [@danwinship](https://github.com/danwinship))
- The `SelfSubjectReview` API is promoted to `authentication.k8s.io/v1` and the `kubectl auth whoami` command is GA. ([#117713](https://github.com/kubernetes/kubernetes/pull/117713), [@nabokihms](https://github.com/nabokihms)) [SIG API Machinery, Architecture, Auth, CLI and Testing]

   ([#123611](https://github.com/kubernetes/kubernetes/pull/123611), [@ritazh](https://github.com/ritazh))
- kube-apiserver: JWT authenticator now reports the following metrics: - apiserver_authentication_config_controller_automatic_reloads_total - apiserver_authentication_config_controller_automatic_reload_last_timestamp_seconds
   ([#123793](https://github.com/kubernetes/kubernetes/pull/123793), [@aramase](https://github.com/aramase))

* client-go: alpha support for out-of-tree exec-based credential providers. For example, a cloud provider could create their own authentication system rather than using the standard authentication provided with Kubernetes. ([#59495](https://github.com/kubernetes/kubernetes/pull/59495), [@ericchiang](https://github.com/ericchiang))

### API Change

- '`kube-apiserver`: adds `--authentication-config` flag for reading `AuthenticationConfiguration`
  files. `--authentication-config` flag is mutually exclusive with the existing `--oidc-*`
  flags.' ([#119142](https://github.com/kubernetes/kubernetes/pull/119142), [@aramase](https://github.com/aramase))

* kube-apiserver: OIDC authentication now supports requiring specific claims with `--oidc-required-claim=<claim>=<value>` Previously, there was no mechanism for a user to specify claims in the OIDC authentication process that were requid to be present in the ID Token with an expected value. This version now makes it possible to require claims support for the OIDC authentication. It allows users to pass in a `--oidc-required-claims` flag, and `key=value`...

* The OpenID Connect authenticator can now use a custom prefix, or omit the default prefix, for username and groups claims through the --oidc-username-prefix and --oidc-groups-prefix flags. For example, the authenticator can map a user with the username "jane" to "google:jane" by supplying the "google:" username prefix. ([#50875](https://github.com/kubernetes/kubernetes/pull/50875),...