* [beta] Kubelet certificate rotation through the certificates API has been promoted from alpha to beta. RBAC cluster roles for the certificates controller have been added for common uses of the certificates API, such as the kubelet's.

previously created the first bootstrap client credentials in the certificates directory as `kubelet-client.key` and `kubelet-client.crt`.  Subsequent certificates created by cert rotation were created in a combined PEM file that was atomically rotated as `kubelet-client-DATE.pem` in that directory, which meant clients relying on the `node.kubeconfig` generated by bootstrapping would never use a rotated cert.  The initial bootstrap certificate is now generated into the cert directory as a PEM file and symlinked...

    * configuration scripts to allow configuration of signing duration of
    * certificates issued via the Certificate Signing Request API.

  - Some kubeadm commands are now allowed to work in a completely offline mode.
- Certificate handling improvements:
  - Renew certs as part of upgrade.
  - New `kubeadm alpha phase certs renew` command for renewing certificates.
  - Certificates created with kubeadm now have improved uniqueness of Distinguished Name fields.
- HA improvements:

- Added two client certificate metrics for exec auth:
    - `rest_client_certificate_expiration_seconds` a gauge reporting the lifetime of the current client certificate. Reports the time of expiry in seconds since January 1, 1970 UTC.

Prior to 1.17 and for existing nodes created by `kubeadm init` where kubelet client certificate rotation is desired, you must modify `/etc/kubernetes/kubelet.conf` to point to the PEM symlink for rotation:

- Kubeadm: add support for certificate chain validation. When using kubeadm in external CA mode, this allows an intermediate CA to be used to sign the certificates. The intermediate CA certificate must be appended to each signed certificate for this to work correctly. ([#97266](https://github.com/kubernetes/kubernetes/pull/97266), [@robbiemcmichael](https://github.com/robbiemcmichael))...

* Allows extension API server to dynamically discover the requestheader CA certificate when the core API server doesn't use certificate based authentication for it's clients ([#66394](https://github.com/kubernetes/kubernetes/pull/66394), [@rtripat](https://github.com/rtripat))

- When `--rotate-server-certificates` is enabled, kubelet will no longer request a new certificate on startup if the current certificate on disk is satisfactory. ([#69991](https://github.com/kubernetes/kubernetes/pull/69991), [@agunnerson-ibm](https://github.com/agunnerson-ibm))

- Fixes an issue where the vsphere cloud provider will not trust a certificate if:
  - The issuer of the certificate is unknown (x509.UnknownAuthorityError)
  - The requested name does not match the set of authorized names (x509.HostnameError)