### ConfigMap
* Volumes and environment variables populated from ConfigMap and Secret objects can now tolerate the named source object or specific keys being missing, by adding `optional: true` to the volume or environment variable source specifications. ([#39981](https://github.com/kubernetes/kubernetes/pull/39981), [@fraenkel](https://github.com/fraenkel))

    * If you are running E2E tests which require SSH keys and you utilize environment variables to override their location, you may need to modify the environment variable set. On all providers the environment variable override can now be either an absolute path to the key or a relative path (relative to ~/.ssh). Specifically the changes are:

- KCM specific args can be passed with `/cluster` script, without affecting CCM. New variable name: `KUBE_CONTROLLER_MANAGER_TEST_ARGS`. ([#120524](https://github.com/kubernetes/kubernetes/pull/120524), [@jprzychodzen](https://github.com/jprzychodzen)) [SIG Cloud Provider]

- The certificate signer no longer accepts ca.key passwords via the `CFSSL_CA_PK_PASSWORD` environment variable. This capability was not prompted by user request, never advertised, and recommended against in the security audit. ([#84677](https://github.com/kubernetes/kubernetes/pull/84677), [@mikedanese](https://github.com/mikedanese))

   ([#123341](https://github.com/kubernetes/kubernetes/pull/123341), [@neolit123](https://github.com/neolit123))
- kubectl `port-forward` over websockets (tunneling SPDY) can now be enabled using an `Alpha` feature flag environment variable: KUBECTL_PORT_FORWARD_WEBSOCKETS=true. The API Server being communicated to must *also* have an `Alpha` feature flag enabled: PortForwardWebsockets.

 - Fixed the behavior of the `KUBE_PROXY_NFTABLES_SKIP_KERNEL_VERSION_CHECK` environment variable in the nftables proxier. The kernel version check is now skipped only when this variable is explicitly set to a non-empty value. To skip the check, set the `KUBE_PROXY_NFTABLES_SKIP_KERNEL_VERSION_CHECK` environment variable. ([#130401](https://github.com/kubernetes/kubernetes/pull/130401), [@ryota-sakamoto](https://github.com/ryota-sakamoto))

OpenStack cloud provider can now be specified as environment variables. When we convert the OpenStack cloud provider to run in an external process, we can now use the kubernetes Secrets capability to inject the OS_* variables. This way we can specify the cloud configuration as a configmap, and specify secrets for the userid/password information. The configmap is mounted as a file, and the secrets are made available as environment variables. The external controller itself runs as a pod/daemonset. For...

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

* `hack/local-up-cluster.sh` now enables the Node authorizer by default. Authorization modes can be overridden with the `AUTHORIZATION_MODE` environment variable, and the `ENABLE_RBAC` environment variable is no longer used. ([#49812](https://github.com/kubernetes/kubernetes/pull/49812), [@liggitt](https://github.com/liggitt))

* CUSTOM_KUBE_DASHBOARD_BANNER environment variable will be used to populate notification banner in Kubernetes Dashboard add-on. ([#60639](https://github.com/kubernetes/kubernetes/pull/60639), [@konryd](https://github.com/konryd))