- 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]

- 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)

### Other notable changes

* The kube-apiserver --service-account-key-file option can be specified multiple times, or can point to a file containing multiple keys, to enable rotation of signing keys. ([#34029](https://github.com/kubernetes/kubernetes/pull/34029), [@liggitt](https://github.com/liggitt))

        final byte[] buffer = this.getContext().getBufferCache().getBuffer();
        try {
            // synchronize around encode and write so that the ordering for SMB1 signing can be maintained
            synchronized (this.outLock) {
                final int n = smb.encode(buffer, 4);
                Encdec.enc_uint32be(n & 0xFFFF, buffer, 0); /* 4 byte session message header */

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...

- Added support to the kube-apiserver for an alpha feature enabling external signing of service account tokens and fetching of public verifying keys, by enabling the Alpha `ExternalServiceAccountTokenSigner` feature gate and specifying `--service-account-signing-endpoint`. The flag value can either be the location of a Unix domain socket on a filesystem, or be prefixed with an @ symbol and name a Unix domain socket in...

- 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))

* 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))

* 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

  - [Major Themes](#major-themes)
    - [Dockershim Removed from kubelet](#dockershim-removed-from-kubelet)
    - [Beta APIs Off by Default](#beta-apis-off-by-default)
    - [Signing Release Artifacts](#signing-release-artifacts)
    - [OpenAPI v3](#openapi-v3)
    - [Storage Capacity and Volume Expansion Are Generally Available](#storage-capacity-and-volume-expansion-are-generally-available)