- `--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.

* 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 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))

    - [kubeadm](#kubeadm-1)
    - [Other Deprecations](#other-deprecations)
  - [Changes to API Resources](#changes-to-api-resources)
    - [ABAC](#abac)
    - [Admission Control](#admission-control)
    - [Authentication](#authentication)
    - [Authorization](#authorization)
    - [Autoscaling](#autoscaling-1)
    - [Certificates](#certificates)
    - [ConfigMap](#configmap)
    - [CronJob](#cronjob)
    - [DaemonSet](#daemonset-1)

- github.com/hashicorp/go-syslog: [v1.0.0](https://github.com/hashicorp/go-syslog/tree/v1.0.0)
- github.com/jimstudt/http-authentication: [3eca13d](https://github.com/jimstudt/http-authentication/tree/3eca13d)
- github.com/kisielk/errcheck: [v1.2.0](https://github.com/kisielk/errcheck/tree/v1.2.0)
- github.com/kisielk/gotool: [v1.0.0](https://github.com/kisielk/gotool/tree/v1.0.0)

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"...

 *  New: `EventListener.followUpDecision()` is called each time a response is received. It notifies
    your listener if OkHttp has decided to make a follow-up request. Some common follow-ups are
    authentication challenges and redirects.

 *  New: Handy constants for `Headers.EMPTY`, `RequestBody.EMPTY`, and `ResponseBody.EMPTY`.

 *  New: OkHttp now calls `StrictMode.noteSlowCall()` when initializing TLS on Android. Use

- 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...

- Kube-up now includes CoreDNS version v1.9.3. ([#110488](https://github.com/kubernetes/kubernetes/pull/110488), [@mzaian](https://github.com/mzaian))
- Kubeadm: Added support for additional authentication strategies in `kubeadm join` with discovery/kubeconfig file: client-go authentication plugins (`exec`), `tokenFile`, and `authProvider.` ([#110553](https://github.com/kubernetes/kubernetes/pull/110553), [@tallaxes](https://github.com/tallaxes))

 * no mechanism to differentiate empty from absent. Neither of these components are popular in
 * practice. Typically HTTP applications use other mechanisms for user identification and
 * authentication.
 *
 * ### Host
 *
 * The host identifies the webserver that serves the URL's resource. It is either a hostname like
 * `square.com` or `localhost`, an IPv4 address like `192.168.0.1`, or an IPv6 address like `::1`.