@Override
  public void updateFilteredReadRequests() {
    String user = getActiveUser();
    if (user != null) {
      MetricsUserSource userSource = getOrCreateMetricsUser(user);
      incrementFilteredReadRequests(userSource);
    }
  }
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