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Ratchet PHP WAMP - React / ZeroMQ - Specific user broadcast

Note: This is not the same as this question which utilises MessageComponentInterface. I am using WampServerInterface instead, so this question pertains to that part specifically. I need an answer with code examples and an explanation, as I can see this being helpful to others in the future.

Attempting looped pushes for individual users

I'm using the WAMP part of Ratchet and ZeroMQ, and I currently have a working version of the push integration tutorial.

I'm attempting to perform the following:

The zeromq server is up and running, ready to log subscribers and unsubscribers
A user connects in their browser over the websocket protocol
A loop is started which sends data to the specific user who requested it
When the user disconnects, the loop for that user's data is stopped

I have points (1) and (2) working, however the issue I have is with the third one:

Firstly: How can I send data to each specific user only? Broadcast sends it to everyone, unless maybe the 'topics' end up being individual user IDs maybe?

Secondly: I have a big security issue. If I'm sending which user ID wants to subscribe from the client-side, which it seems like I need to, then the user could just change the variable to another user's ID and their data is returned instead.

Thirdly: I'm having to run a separate php script containing the code for zeromq to start the actual looping. I'm not sure this is the best way to do this and I would rather having this working completely within the codebase as opposed to a separate php file. This is a major area I need sorted.

The following code shows what I currently have.

The server that just runs from console

I literally type php bin/push-server.php to run this. Subscriptions and un-subscriptions are output to this terminal for debugging purposes.

$loop   = React\EventLoop\Factory::create();
$pusher = Pusher;

$context = new React\ZMQ\Context($loop);
$pull = $context->getSocket(ZMQ::SOCKET_PULL);
$pull->bind('tcp://127.0.0.1:5555');
$pull->on('message', array($pusher, 'onMessage'));

$webSock = new React\Socket\Server($loop);
$webSock->listen(8080, '0.0.0.0'); // Binding to 0.0.0.0 means remotes can connect
$webServer = new Ratchet\Server\IoServer(
    new Ratchet\WebSocket\WsServer(
        new Ratchet\Wamp\WampServer(
            $pusher
        )
    ),
    $webSock
);

$loop->run();

The Pusher that sends out data over websockets

I've omitted the useless stuff and concentrated on the onMessage() and onSubscribe() methods.

public function onSubscribe(ConnectionInterface $conn, $topic) 
{
    $subject = $topic->getId();
    $ip = $conn->remoteAddress;

    if (!array_key_exists($subject, $this->subscribedTopics)) 
    {
        $this->subscribedTopics[$subject] = $topic;
    }

    $this->clients[] = $conn->resourceId;

    echo sprintf("New Connection: %s" . PHP_EOL, $conn->remoteAddress);
}

public function onMessage($entry) {
    $entryData = json_decode($entry, true);

    var_dump($entryData);

    if (!array_key_exists($entryData['topic'], $this->subscribedTopics)) {
        return;
    }

    $topic = $this->subscribedTopics[$entryData['topic']];

    // This sends out everything to multiple users, not what I want!!
    // I can't send() to individual connections from here I don't think :S
    $topic->broadcast($entryData);
}

The script to start using the above Pusher code in a loop

This is my issue - this is a separate php file that hopefully may be integrated into other code in the future, but currently I'm not sure how to use this properly. Do I grab the user's ID from the session? I still need to send it from client-side...

// Thought sessions might work here but they don't work for subscription
session_start();
$userId = $_SESSION['userId'];

$loop   = React\EventLoop\Factory::create();

$context = new ZMQContext();
$socket = $context->getSocket(ZMQ::SOCKET_PUSH, 'my pusher');
$socket->connect("tcp://localhost:5555");

$i = 0;
$loop->addPeriodicTimer(4, function() use ($socket, $loop, $userId, &$i) {

   $entryData = array(
       'topic'     => 'subscriptionTopicHere',
       'userId'    => $userId
    );
    $i++;

    // So it doesn't go on infinitely if run from browser
    if ($i >= 3)
    {
        $loop->stop();
    }

    // Send stuff to the queue
    $socket->send(json_encode($entryData));
});

Finally, the client-side js to subscribe with

$(document).ready(function() { 

    var conn = new ab.Session(
        'ws://localhost:8080' 
      , function() {            
            conn.subscribe('topicHere', function(topic, data) {
                console.log(topic);
                console.log(data);
            });
        }
      , function() {          
            console.warn('WebSocket connection closed');
        }
      , {                       
            'skipSubprotocolCheck': true
        }
    );
});

Conclusion

The above is working, but I really need to figure out the following:

How can I send individual messages to individual users? When they visit the page that starts the websocket connection in JS, should I also be starting the script that shoves stuff into the queue in PHP (the zeromq)? That's what I'm currently doing manually, and it just feels wrong.
When subscribing a user from JS, it can't be safe to grab the users id from the session and send that from client-side. This could be faked. Please tell me there is an easier way, and if so, how?