* 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.

* 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))

- Kubeadm: add support for certificate chain validation. When using kubeadm in external CA mode, this allows an intermediate CA to be used to sign the certificates. The intermediate CA certificate must be appended to each signed certificate for this to work correctly. ([#97266](https://github.com/kubernetes/kubernetes/pull/97266), [@robbiemcmichael](https://github.com/robbiemcmichael)) [SIG Cluster Lifecycle]

  - The requested name does not match the set of authorized names (x509.HostnameError)
  - The error surfaced after attempting a connection contains one of the substrings: "certificate is not trusted" or "certificate signed by unknown authority" ([#120767](https://github.com/kubernetes/kubernetes/pull/120767), [@MadhavJivrajani](https://github.com/MadhavJivrajani)) [SIG Architecture and Cloud Provider]

* 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.

- consumers of the 'certificatesigningrequests/approval' API must now have permission to 'approve' CSRs for the specific signer requested by the CSR. More information on the new signerName field and the required authorization can be found at https://kubernetes.io/docs/reference/access-authn-authz/certificate-signing-requests#authorization ([#88246](https://github.com/kubernetes/kubernetes/pull/88246), [@munnerz](https://github.com/munnerz)) [SIG API Machinery, Apps,...

- 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)

### 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))

  - The requested name does not match the set of authorized names (x509.HostnameError)
  - The error surfaced after attempting a connection contains one of the substrings: "certificate is not trusted" or "certificate signed by unknown authority" ([#120768](https://github.com/kubernetes/kubernetes/pull/120768), [@MadhavJivrajani](https://github.com/MadhavJivrajani)) [SIG Architecture and Cloud Provider]

For detailed release notes on the three alpha features from SIG AWS, please refer to the following Changelogs: