How to validate POST data in Silex with Pomm

application.php

<?php application.php
// ...
$app->post('/tasks/new', function() use ($app) {
    $task_map = $app['pomm.connection']
                    ->getMapFor('\Taf\Task\Task');

    $new_task = new Validation\NewTask($app['request']->request->get('new_task'));
    $new_task->worker_id = $app['taf.session']->getWorkerId();

    if (count($app['validator']->validate($new_task)) == 0)
    {
        $task = $task_map->createAndSaveObject((array) $new_task);

        return $app->json(array('task' => $task->extract()), 201);
    }

    return new Response('Invalid or missing parameters.', 400);
})->before($check_token);