- Adds feature gate `KubeletInUserNamespace` which enables support for running kubelet in a user namespace.
  
  The user namespace has to be created before running kubelet.
  All the node components such as CRI need to be running in the same user namespace.
  

* The `--authorization-rbac-super-user` flag (alpha in 1.5) is deprecated; the `system:masters` group has privileged access ([#38121](https://github.com/kubernetes/kubernetes/pull/38121), [@deads2k](https://github.com/deads2k))

    * for the kubelet is used, and is expected to be present in `/var/lib/kubelet/config.yaml`.
    * For runtime-detected, instance-specific configuration values, a environment file with
    * dynamically-generated flags at `kubeadm init` or `kubeadm join` run time is used.
    * Finally, if the user wants to override something specific for the kubelet that can't be done via

- kubeadm: make the command "kubeadm alpha kubeconfig user" accept a "--config" flag and remove the following flags:
  - apiserver-advertise-address / apiserver-bind-port: use either localAPIEndpoint from InitConfiguration or controlPlaneEndpoint from ClusterConfiguration.
  - cluster-name: use clusterName from ClusterConfiguration

- Kubeadm: graduate the command `kubeadm alpha kubeconfig user` to `kubeadm kubeconfig user`. The `kubeadm alpha kubeconfig user` command is deprecated now. ([#97583](https://github.com/kubernetes/kubernetes/pull/97583), [@knight42](https://github.com/knight42)) [SIG Cluster Lifecycle]

- Kubeadm: `kubeadm upgrade node` now supports `addon` and `post-upgrade` phases. User can use `kubeadm upgrade node phase addon` to execute the addon upgrade, or use `kubeadm upgrade node --skip-phases addon` to skip the addon upgrade. Currently, the `post-upgrade` phase is no-op, and it is mainly used to handle some release specific post-upgrade tasks. ([#127242](https://github.com/kubernetes/kubernetes/pull/127242), [@SataQiu](https://github.com/SataQiu))...

* `kubectl create rolebinding` and `kubectl create clusterrolebinding` invocations must be updated to  specify multiple subjects as repeated  `--user`, `--group`, or `--serviceaccount` arguments instead of comma-separated arguments to a single `--user`, `--group`, or `--serviceaccount`.  E.g. `--user=x,y` must become `--user x --user y`  ([#43903](https://github.com/kubernetes/kubernetes/pull/43903), [@xilabao](https://github.com/xilabao))


### kubeadm

  - `alpha` support (guarded by the `ServiceAccountTokenPodNodeInfo` feature gate) for including the node name (and uid, if the node exists) as additional claims in service account tokens it issues which are bound to pods, and `authentication.kubernetes.io/node-name` and `authentication.kubernetes.io/node-uid` extra user info when the token is used to authenticate.

- Removed a warning around Linux user namespaces and kernel version. If the feature gate `UserNamespacesSupport` was enabled, the kubelet previously warned when detecting a Linux kernel version earlier than 6.3.0. User namespace support on Linux typically does still need kernel 6.3 or...

* [beta] SelfSubjectRulesReview, an API that lets a user see what actions they can perform with a namespace, has been added to the authorization.k8s.io API group. This bulk query is intended to enable UIs to show/hide actions based on the end user, and for users to quickly reason about their own permissions.