### Action Required

* action required: the API server and client-go libraries have been fixed to support additional non-alpha-numeric characters in UserInfo "extra" data keys. Both should be updated in order to properly support extra data containing "/" characters or other characters disallowed in HTTP headers. ([#65799](https://github.com/kubernetes/kubernetes/pull/65799), [@dekkagaijin](https://github.com/dekkagaijin))

### Auth

- Fixed OpenID Connect (OIDC) token refresh when the client secret contains a special character. ([#76914](https://github.com/kubernetes/kubernetes/pull/76914), [@tsuna](https://github.com/tsuna))

### Action Required

* action required: the API server and client-go libraries have been fixed to support additional non-alpha-numeric characters in UserInfo "extra" data keys. Both should be updated in order to properly support extra data containing "/" characters or other characters disallowed in HTTP headers. ([#65799](https://github.com/kubernetes/kubernetes/pull/65799), [@dekkagaijin](https://github.com/dekkagaijin))

### Action Required

* action required: the API server and client-go libraries have been fixed to support additional non-alpha-numeric characters in UserInfo "extra" data keys. Both should be updated in order to properly support extra data containing "/" characters or other characters disallowed in HTTP headers. ([#65799](https://github.com/kubernetes/kubernetes/pull/65799), [@dekkagaijin](https://github.com/dekkagaijin))

    <_comment>Based on TIKA-2469, we've added a heuristic/wild guess that the first 10 chars</_comment>
    <_comment>after the length byte should be \x00 or a non-control character.</_comment>
    <magic priority="80">
      <match value="(?s)^([\\x05-\\x0F])[\\x00\\x20-\\x7E]{10}.{43}\\1\x00" type="regex" offset="0"/>
    </magic>
  </mime-type>
  <mime-type type="application/x-ms-nls">

- The etcd client library vendored in v1.16 (github.com/coreos/etcd/clientv3) has a bug where IPv6 IP addresses get incorrectly trimmed to the first occurance of the `:` character. This affects all users of the client library including the kube-apiserver and kubeadm. We are targeting the fix for this bug in v1.16.3. ([#83550](https://github.com/kubernetes/kubernetes/issues/83550))

## Urgent Upgrade Notes

- Fixed EndpointSlice port name validation to match Endpoint port name validation (allowing port names longer than 15 characters) ([#84481](https://github.com/kubernetes/kubernetes/pull/84481), [@robscott](https://github.com/robscott))

- The API server and client-go libraries have been fixed to support additional non-alpha-numeric characters in UserInfo "extra" data keys. Both should be updated in order to properly support extra data containing "/" characters or other characters disallowed in HTTP headers. ([#65799](https://github.com/kubernetes/kubernetes/pull/65799), [@dekkagaijin](https://github.com/dekkagaijin)) Courtesy of SIG Auth

- Kubeadm: external etcd endpoints passed in the `ClusterConfiguration` that have Unicode characters are no longer IDNA encoded (converted to Punycode). They are now just URL encoded as per Go's implementation of RFC-3986, have duplicate "/" removed from the URL paths, and passed like that directly to the `kube-apiserver` `--etcd-servers` flag. If you have etcd endpoints that have Unicode characters, it is advisable to encode them in advance with tooling that is fully IDNA compliant. If you don't...

- Added support for CEL expressions with escaped names in the structured authentication config. Using `[...]` to access claims or user data was recommended when names contained characters that would otherwise need escaping. CEL optionals with `?` could be used where has was not applicable — for example, `claims[?"kubernetes.io"]` or `user.extra[?"domain.io/foo"]`. ([#131574](https://github.com/kubernetes/kubernetes/pull/131574),...