code: private static void checkSecurityEnabled(AuthType authType) {
      // TODO(dong): add Kerberos condition check.
      if (authType != AuthType.SIMPLE && authType != AuthType.CUSTOM) {
        throw new UnsupportedOperationException("User is not supported in " + authType.getAuthName()
            + " mode");
      }
    }
docs: Checks whether Alluxio is running in secure mode, such as {@link AuthType#SIMPLE},
  {@link AuthType#KERBEROS}, {@link AuthType#CUSTOM}.
  
  @param authType the authentication type in configuration