private List<String> getGroupNames() {
    SessionState ss = SessionState.get();
    if (ss != null && ss.getAuthenticator() != null) {
      return ss.getAuthenticator().getGroupNames();
    }
    return null;
  }
@return the metastore client for the current thread
@throws MetaException
ql/src/java/org/apache/hadoop/hive/ql/metadata/Hive.java