- Added authorization check support to the CEL expressions of ValidatingAdmissionPolicy via a `authorizer`

Security enhancements in this release include encrypted secrets (alpha), network policy for pod-to-pod communication, the node authorizer to limit Kubelet access to API resources, and Kubelet client / server TLS certificate rotation (alpha).

* kube-up: increase download timeout for kubernetes.tar.gz ([#29426](https://github.com/kubernetes/kubernetes/pull/29426), [@justinsb](https://github.com/justinsb))
* Fix RBAC authorizer of ServiceAccount ([#29071](https://github.com/kubernetes/kubernetes/pull/29071), [@albatross0](https://github.com/albatross0))

* Fix working_set calculation in kubelet ([#29153](https://github.com/kubernetes/kubernetes/pull/29153), [@vishh](https://github.com/vishh))
* Fix RBAC authorizer of ServiceAccount ([#29071](https://github.com/kubernetes/kubernetes/pull/29071), [@albatross0](https://github.com/albatross0))

* The SubjectAccessReview API passes subresource and resource name information to the authorizer to answer authorization queries. ([#40935](https://github.com/kubernetes/kubernetes/pull/40935), [@liggitt](https://github.com/liggitt))

* RBAC: all configured authorizers are now checked to determine if an RBAC role or clusterrole escalation (setting permissions the user does not currently have via RBAC) is allowed. ([#56358](https://github.com/kubernetes/kubernetes/pull/56358), [@liggitt](https://github.com/liggitt))...

adds an alpha AuthorizeNodeWithSelectors feature that makes the node authorizer limit requests from node API clients to get / list / watch its own Node API object, and to get / list / watch its own Pod API objects. Clients using kubelet credentials to read other nodes or unrelated pods must change their authentication credentials (recommended), adjust their usage, or grant broader read access independent of the node authorizer. ([#125571](https://github.com/kubernetes/kubernetes/pull/125571), [@...

[API Aggregation](https://github.com/kubernetes/enhancements/issues/263) has been upgraded to "stable" in Kubernetes 1.10, so you can use it in production. Webhooks have seen numerous improvements, including alpha [Support for self-hosting authorizer webhooks](https://github.com/kubernetes/enhancements/issues/516).

### Auth

* Resolves error from v1.17.0-beta.2 with --authorizer-mode webhook complaining about an invalid version ([#85441](https://github.com/kubernetes/kubernetes/pull/85441), [@liggitt](https://github.com/liggitt))

- Add node_authorizer_actions_duration_seconds metric that can be used to estimate load to node authorizer. ([#92466](https://github.com/kubernetes/kubernetes/pull/92466), [@mborsz](https://github.com/mborsz)) [SIG API Machinery, Auth and Instrumentation]