// +optional
  optional string user = 5;

  // keyring is the path to key ring for RBDUser.
  // Default is /etc/ceph/keyring.
  // More info: https://examples.k8s.io/volumes/rbd/README.md#how-to-use-it
  // +optional
  optional string keyring = 6;

  // secretRef is name of the authentication secret for RBDUser. If provided
  // overrides keyring.
  // Default is nil.