- The default Bootstrap Token created with `kubeadm init` v1.8 expires
 and is deleted after 24 hours by default to limit the exposure of the
 valuable credential. You can create a new Bootstrap Token with
 `kubeadm token create` or make the default token permanently valid by specifying
 `--token-ttl 0` to `kubeadm init`. The default token can later be deleted with
 `kubeadm token delete`.

`kube-controller-manager`: The `LegacyServiceAccountTokenCleanUp` feature gate is now `beta` and enabled by default. When enabled, legacy auto-generated service account token secrets are auto-labeled with a `kubernetes.io/legacy-token-invalid-since` label if the credentials have not been used in the time specified by `--legacy-service-account-token-clean-up-period` (defaulting to one year), **and** are referenced from the `.secrets` list of a ServiceAccount object, **and**  are not referenced from pods. This...

  - This changes the tokens provided to containers at `/var/run/secrets/kubernetes.io/serviceaccount/token` to be time-limited, auto-refreshed, and invalidated when the containing pod is deleted.
  - Clients should reload the token from disk periodically (once per minute is recommended) to ensure they continue to use a valid token. `k8s.io/client-go` version v11.0.0+ and v0.15.0+ reload tokens automatically.

- kube-apiserver: `--service-account-max-token-expiration` can now be used in combination with an external token signer `--service-account-signing-endpoint`, as long as the `--service-account-max-token-expiration` is not longer than the external token signer's max expiration. ([#129816](https://github.com/kubernetes/kubernetes/pull/129816), [@sambdavidson](https://github.com/sambdavidson)) [SIG...

- Fixes service account token admission error in clusters that do not run the service account token controller ([#87029](https://github.com/kubernetes/kubernetes/pull/87029), [@liggitt](https://github.com/liggitt)) [SIG Auth]

  * All communication is now over TLS
  * Authorization plugins can be installed by kubeadm, including the new default of RBAC
  * The bootstrap token system now allows token management and expiration
* The [`kubefed` federation bootstrap tool](https://kubernetes.io/docs/tutorials/federation/set-up-cluster-federation-kubefed/) has also graduated to beta.

- Kube-apiserver can now specify `--authentication-token-webhook-version=v1` or `--authorization-webhook-version=v1` to use `v1` TokenReview and SubjectAccessReview API objects when communicating with authentication and authorization webhooks. ([#84768](https://github.com/kubernetes/kubernetes/pull/84768), [@liggitt](https://github.com/liggitt))

### **Cluster Lifecycle**

*   You must either specify the `--discovery-token-ca-cert-hash` flag to `kubeadm join`, or opt out of the CA pinning feature using `--discovery-token-unsafe-skip-ca-verification`.
*   The default `auto-detect` behavior of the kubelet's `--cloud-provider` flag is removed.

* `--service-account-lookup` now defaults to true, requiring the Secret API object containing the token to exist in order for a service account token to be valid. This enables service account tokens to be revoked by deleting the Secret object containing the token. ([#44071](https://github.com/kubernetes/kubernetes/pull/44071), [@liggitt](https://github.com/liggitt))

### VMware

- SAML token delegation (required for Zones support in vSphere) is now supported ([#78876](https://github.com/kubernetes/kubernetes/pull/78876), [@dougm](https://github.com/dougm))
- vSphere SAML token auth is now supported when using Zones ([#75515](https://github.com/kubernetes/kubernetes/pull/75515), [@dougm](https://github.com/dougm))