Connect to Elastic Cloud via PreBuiltXPackTransportClient

[occurred (Charlie)]

I was following the instructions from here:
https://www.elastic.co/guide/en/x-pack/current/java-clients.html

and just for my initial tests I've used the following example:

import org.elasticsearch.xpack.client.PreBuiltXPackTransportClient;

TransportClient client = new PreBuiltXPackTransportClient(Settings.builder()
    .put("cluster.name", "myClusterName")
    .put("xpack.security.user", "transport_client_user:x-pack-test-password")
    ...
    .build())

I'm adding the transport address like this (attention it's groovy code ):

InetAddress.getAllByName("elasticSearchAPIEndpoint_found_at_https://cloud.elastic.co/").each { address ->
    if ((address instanceof Inet6Address) || (address instanceof Inet4Address)) {
        client.addTransportAddress(new InetSocketTransportAddress(address, 9243))
    }
}

Of course with the correct address to my cloud instance and my correct xpack.security.user, also have created a new user in Kibana with role "transport_client".
ES version is 5.6.1
x-pack-transport: 5.6.1

These are the settings I can see when debugging:

My result for connectedNodes() is always empty.

[occurred (Charlie)]

My solution is the following:
https://www.elastic.co/guide/en/elasticsearch/client/java-rest/6.4/_basic_authentication.html

It seems there is no way to get it working in the older versions...