@Override
    public Properties getCredentials(Properties securityProps, DistributedMember server,
        boolean isPeer) throws AuthenticationFailedException {
      String userName = securityProps.getProperty(USER_NAME);
      if (userName == null) {
        throw new AuthenticationFailedException(
            "TestPeerAuthInitialize: The user name property [" + USER_NAME + "] not set");
      }

      Properties newProps = new Properties();
      newProps.setProperty(USER_NAME, userName);

      String passwd = securityProps.getProperty(PASSWORD);
      if (passwd == null) {
        throw new AuthenticationFailedException(
            "TestPeerAuthInitialize: The password property [" + PASSWORD + "] not set");
      }
      newProps.setProperty(PASSWORD, passwd);

      System.out.println(Thread.currentThread().getName()
          + ": TestPeerAuthInitialize providing credentials for " + (isPeer ? "peer " : "client ")
          + server + ": " + newProps + " at " + System.currentTimeMillis());

      return newProps;
    }
Use of SECURITY_CLIENT_AUTHENTICATOR should result in the servers performing authentication
during HandShake of Gateway Sender/Receiver connecting.
geode-wan/src/distributedTest/java/org/apache/geode/internal/cache/wan/GatewayLegacyAuthenticationRegressionTest.java