* Websocket requests may now authenticate to the API server by passing a bearer token in a websocket subprotocol of the form `base64url.bearer.authorization.k8s.io.<base64url-encoded-bearer-token>`. ([#47740](https://github.com/kubernetes/kubernetes/pull/47740), [@liggitt](https://github.com/liggitt))

* Added a new secret type "bootstrap.kubernetes.io/token" for dynamically creating TLS bootstrapping bearer tokens. ([#41281](https://github.com/kubernetes/kubernetes/pull/41281), [@ericchiang](https://github.com/ericchiang))

### Service

- kubeadm: Added better handling of errors during unmount when calling `kubeadm reset`. When failing to unmount directories under `/var/run/kubelet`, kubeadm will now throw an error instead of showing a warning and continuing to clean up said directory. In such situations, it is better for you to inspect the problem and resolve it manually. Then, you can call `kubeadm reset` again to complete the cleanup....

### Other (Cleanup or Flake)

- Client-go header logging (at verbosity levels >= 9) now masks `Authorization` header contents ([#95316](https://github.com/kubernetes/kubernetes/pull/95316), [@sfowl](https://github.com/sfowl)) [SIG API Machinery]

## Dependencies

### Added
_Nothing has changed._

  - Different configuration types can be supplied all in the same file separated by `---`.
- Improved CRI handling
  - crictl is no longer required in docker-only setups.
  - Better detection of installed CRI.
  - Better output for image pull errors.
- Improved air-gapped and offline support
  - kubeadm now handles air-gapped environments by using the local client version as a fallback.

- Kubeadm: waiting for etcd learner member to be started before promoting during 'kubeadm join' ([#136366](https://github.com/kubernetes/kubernetes/pull/136366), [@dlipovetsky](https://github.com/dlipovetsky)) [SIG Cluster Lifecycle]

- Kube API server accepts `Impersonate-Uid` header to impersonate a user with a specific UID, in the same way that you can currently use `Impersonate-User`, `Impersonate-Group`...

## Changelog since v1.35.2

## Changes by Kind

### Bug or Regression

- Kubeadm: do not add learner member to etcd client endpoints ([#137257](https://github.com/kubernetes/kubernetes/pull/137257), [@ahrtr](https://github.com/ahrtr)) [SIG Cluster Lifecycle]

* kube-scheduler: restores default leader election behavior. leader-elect command line parameter should "true" ([#60524](https://github.com/kubernetes/kubernetes/pull/60524), [@dims](https://github.com/dims))

- Added a path `/header?key=` to `agnhost netexec` allowing one to view what the header value is of the incoming request.

  Ex:
  ```
  $ curl -H "X-Forwarded-For: something" 172.17.0.2:8080/header?key=X-Forwarded-For
  something
  ```