@Override
  public void preStopMaster(ObserverContext<MasterCoprocessorEnvironment> c) {
    if (initialized) {
      hdfsAclHelper.close();
    }
  }
Provider for mapping principal names to Users
hbase-server/src/main/java/org/apache/hadoop/hbase/security/access/SnapshotScannerHDFSAclController.java