// More details are available at https://k8s.io/docs/reference/access-authn-authz/certificate-signing-requests/#kubernetes-signers
  //
  // Custom signerNames can also be specified. The signer defines:
  //  1. Trust distribution: how trust (CA bundles) are distributed.
  //  2. Permitted subjects: and behavior when a disallowed subject is requested.

  //  2. If it's a kubelet serving certificate, it is assigned
  //     "kubernetes.io/kubelet-serving".
  //  3. Otherwise, it is assigned "kubernetes.io/legacy-unknown".
  // Distribution of trust for signers happens out of band.
  // You can select on this field using `spec.signerName`.
  // +optional
  optional string signerName = 7;