@Override
  public OperationStatus[] addLabels(List<byte[]> labels) throws IOException {
    // Not doing specific label add. We will just add labels in Mutation
    // visibility expression as it
    // is along with every cell.
    OperationStatus[] status = new OperationStatus[labels.size()];
    for (int i = 0; i < labels.size(); i++) {
      status[i] = new OperationStatus(OperationStatusCode.SUCCESS);
    }
    return status;
  }
This is a VisibilityLabelService where labels in Mutation's visibility expression will be
persisted as Strings itself rather than ordinals in 'labels' table. Also there is no need to add
labels to the system, prior to using them in Mutations/Authorizations.
hbase-server/src/test/java/org/apache/hadoop/hbase/security/visibility/ExpAsStringVisibilityLabelServiceImpl.java