@InterfaceAudience.Private
  public static boolean isGroupPrincipal(String name) {
    return name != null && name.startsWith(GROUP_PREFIX);
  }
Returns whether or not the given name should be interpreted as a group principal. Currently
this simply checks if the name starts with the special group prefix character ("@").
hbase-common/src/main/java/org/apache/hadoop/hbase/AuthUtil.java