* 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))

* PodSecurityPolicies can now specify a whitelist of allowed paths for host volumes. ([#50212](https://github.com/kubernetes/kubernetes/pull/50212), [@jhorwit2](https://github.com/jhorwit2))

* 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))

Node API object](https://kubernetes.io/docs/reference/access-authn-authz/admission-controllers/#noderestriction). In authentication, we added alpha-level support for automounting improved service account tokens through projected volumes. We also enabled [audience validation in TokenReview](https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.13/#tokenreview-v1-authentication-k8s-io) for the new tokens for improved scoping. Under audit logging, the new alpha-level "dynamic audit configuration"...

* Allows extension API server to dynamically discover the requestheader CA certificate when the core API server doesn't use certificate based authentication for it's clients ([#66394](https://github.com/kubernetes/kubernetes/pull/66394), [@rtripat](https://github.com/rtripat))

- 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...

- Fixed authentication_duration_seconds metric scope. Previously, it included whole apiserver request duration which yields inaccurate results. ([#99944](https://github.com/kubernetes/kubernetes/pull/99944), [@marseel](https://github.com/marseel))

- The Kubernetes API server now correctly detects and closes existing TLS connections when its client certificate file for kubelet authentication has been rotated. ([#115315](https://github.com/kubernetes/kubernetes/pull/115315), [@enj](https://github.com/enj)) [SIG API Machinery, Auth, Node and Testing]

  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]

- Structured Authentication Configuration now supports configuring multiple JWT authenticators. The maximum allowed JWT authenticators in the authentication configuration is 64. ([#123431](https://github.com/kubernetes/kubernetes/pull/123431), [@aramase](https://github.com/aramase))

  - `--address`
  The insecure port flags `--port` may only be set to 0 now.
  
  In addtion, please be careful that:
  - controller-manager MUST start with `--authorization-kubeconfig` and `--authentication-kubeconfig` correctly set to get authentication/authorization working.
  - liveness/readiness probes to controller-manager MUST use HTTPS now, and the default port has been changed to 10257.