This commit is the main API piece of KEP-3257 (ClusterTrustBundles).
This commit:
* Adds the certificates.k8s.io/v1alpha1 API group
* Adds the ClusterTrustBundle type.
* Registers the new type in kube-apiserver.
* Implements the type-specfic validation specified for
ClusterTrustBundles:
- spec.pemTrustAnchors must always be non-empty.
- spec.signerName must be either empty or a valid signer name.
- Changing spec.signerName is disallowed.
* Implements the "attest" admission check to restrict actions on
ClusterTrustBundles that include a signer name.
Because it wasn't specified in the KEP, I chose to make attempts to
update the signer name be validation errors, rather than silently
ignored.
I have tested this out by launching these changes in kind and
manipulating ClusterTrustBundle objects in the resulting cluster using
kubectl.
