@Override
  public String getDisplayString(String[] children) {
    return "CURRENT_GROUPS()";
  }
UDF to get current group from authenticator. This function is not a deterministic function,
but a runtime constant. The return value is constant within a query but can be different between queries.
ql/src/java/org/apache/hadoop/hive/ql/udf/generic/GenericUDFCurrentGroups.java