- Kubeadm: during the validation of existing kubeconfig files on disk, handle cases where the "ca.crt" is a bundle and has intermediate certificates. Find a common trust anchor between the "ca.crt" bundle and the CA in the existing kubeconfig on disk instead of treating "ca.crt" as a file containing a single CA. ([#123102](https://github.com/kubernetes/kubernetes/pull/123102), [@astundzia](https://github.com/astundzia))

- Kubeadm: removed the restriction that the `ca.crt` can only contain one certificate. If there is more than one certificate in the `ca.crt` file, kubeadm will pick the first one by default. ([#107327](https://github.com/kubernetes/kubernetes/pull/107327), [@SataQiu](https://github.com/SataQiu))

* The `--bootstrap-kubeconfig` argument to Kubelet previously created the first bootstrap client credentials in the certificates directory as `kubelet-client.key` and `kubelet-client.crt`.  Subsequent certificates created by cert rotation were created in a combined PEM file that was atomically rotated as `kubelet-client-DATE.pem` in that directory, which meant clients relying on the `node.kubeconfig` generated by bootstrapping would...

- Kubeadm: changed the "system:masters" Group in the apiserver-kubelet-client.crt certificate Subject to be "kubeadm:cluster-admins" which is a less privileged Group. ([#121837](https://github.com/kubernetes/kubernetes/pull/121837), [@neolit123](https://github.com/neolit123))

### Introducing `RootCAConfigMap`

`RootCAConfigMap` graduates to Beta, separating from `BoundServiceAccountTokenVolume`. The `kube-root-ca.crt` ConfigMap is now available to every namespace, by default. It contains the Certificate Authority bundle for verify kube-apiserver connections.

### `kubectl debug` graduates to Beta

- E2e tests wait for kube-root-ca.crt to be populated in namespaces for use with projected service account tokens, reducing delays starting those test pods and errors in the logs. ([#108860](https://github.com/kubernetes/kubernetes/pull/108860), [@eddiezane](https://github.com/eddiezane))...