@Override
  public MetricsUserAggregateSource getSource() {
    return source;
  }
Returns the active user to which authorization checks should be applied. If we are in the
context of an RPC call, the remote user is used, otherwise the currently logged in user is
used.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MetricsUserAggregateImpl.java