code: func (ca *CertAuthorityV2) Checkers() ([]ssh.PublicKey, error) {
  	out := make([]ssh.PublicKey, 0, len(ca.Spec.CheckingKeys))
  	for _, keyBytes := range ca.Spec.CheckingKeys {
  		key, _, _, _, err := ssh.ParseAuthorizedKey(keyBytes)
  		if err != nil {
  			return nil, trace.BadParameter("invalid authority public key (len=%d): %v", len(keyBytes), err)
  		}
  		out = append(out, key)
  	}
  	return out, nil
  }
docs: // Checkers returns public keys that can be used to check cert authorities