* Add CLUSTER_SIGNING_DURATION environment variable to cluster ([#52497](https://github.com/kubernetes/kubernetes/pull/52497), [@jcbsmpsn](https://github.com/jcbsmpsn))
    * configuration scripts to allow configuration of signing duration of
    * certificates issued via the Certificate Signing Request API.

* Add CLUSTER_SIGNING_DURATION environment variable to cluster ([#52497](https://github.com/kubernetes/kubernetes/pull/52497), [@jcbsmpsn](https://github.com/jcbsmpsn))
    * configuration scripts to allow configuration of signing duration of
    * certificates issued via the Certificate Signing Request API.

- The kube-controller-manager managed signers can now have distinct signing certificates and keys.  See the help about `--cluster-signing-[signer-name]-{cert,key}-file`.  `--cluster-signing-{cert,key}-file` is still the default. ([#90822](https://github.com/kubernetes/kubernetes/pull/90822), [@deads2k](https://github.com/deads2k)) [SIG API Machinery, Apps and Auth]

kube-controller-manager has dropped support for the `--insecure-experimental-approve-all-kubelet-csrs-for-group` flag. It is accepted in 1.7, but ignored. Instead, the csrapproving controller uses authorization checks to determine whether to approve certificate signing requests: ([#45619](https://github.com/kubernetes/kubernetes/pull/45619), [@mikedanese](https://github.com/mikedanese))

    * Before upgrading, users must ensure their controller manager will enable the csrapproving controller, create...

    * OverrideSeparator string Delimiter to use to separate region of occurrence, url and signing region for each override Defaults to ","
    * ServiceOverrides string example: s3|region1, https://s3.foo.bar, some signing_region & ec2|region2, https://ec2.foo.bar, signing_region

- Kubeadm: warn but do not error out on missing "ca.key" files for root CA, front-proxy CA and etcd CA, during "kubeadm join --control-plane" if the user has provided all certificates, keys and kubeconfig files which require signing with the given CA keys. ([#94988](https://github.com/kubernetes/kubernetes/pull/94988), [@neolit123](https://github.com/neolit123)) [SIG Cluster Lifecycle]

### Other (Cleanup or Flake)

* kube-apiserver: the OpenID Connect authenticator can now verify ID Tokens signed with JOSE algorithms other than RS256 through the --oidc-signing-algs flag. ([#58544](https://github.com/kubernetes/kubernetes/pull/58544), [@ericchiang](https://github.com/ericchiang))

- The kube-controller-manager's deprecated `--experimental-cluster-signing-duration` flag is now removed. Adapt your machinery to use the `--cluster-signing-duration` flag that is available since v1.19. ([#108476](https://github.com/kubernetes/kubernetes/pull/108476), [@ialidzhikov](https://github.com/ialidzhikov))

* Removed alpha functionality that allowed the controller manager to approve kubelet server certificates. This functionality should be replaced by automating validation and approval of node server certificate signing requests. ([#62471](https://github.com/kubernetes/kubernetes/pull/62471), [@mikedanese](https://github.com/mikedanese))

#### Graduated to Stable/GA

### SIG Auth

- TokenRequest and TokenRequestProjection are now beta features. To enable these feature, the API server needs to be started with the `--service-account-issuer`, `--service-account-signing-key-file`, and `--service-account-api-audiences` flags.
([#67349](https://github.com/kubernetes/kubernetes/pull/67349), [@mikedanese](https://github.com/mikedanese))