title: Get refresh token with FOSOAuthServerBundle
body: <p>When asking for the access token using a url like this (client credentials as grant type):</p>
  
  <pre><code>http://api.local/app_dev.php/oauth/v2/token?client_id=&lt;client_id&gt;&amp;client_secret=&lt;secret&gt;&amp;grant_type=client_credentials
  </code></pre>
  
  <p>I get the following json response:</p>
  
  <pre><code>{
  access_token: "XXXXXXXXXXX",
  expires_in: 3600,
  token_type: "bearer",
  scope: "user"
  }
  </code></pre>
  
  <p>The refresh token is missing, any idea why this could be?</p>
  
  <p>My FOSOAuthServerBundle in config.yml:</p>
  
  <pre><code>fos_oauth_server:
      db_driver: orm
      client_class:        Acme\ApiBundle\Entity\Client
      access_token_class:  Acme\ApiBundle\Entity\AccessToken
      refresh_token_class: Acme\ApiBundle\Entity\RefreshToken
      auth_code_class:     Acme\ApiBundle\Entity\AuthCode
      service:
          user_provider: platform.user.provider
          options:
              supported_scopes: user
  </code></pre>
  
  <p><strong>UPDATE</strong></p>
  
  <p>The Client Entity makes a call to the constructor in the parent entity (located in the FOSOAuthServerBundle):</p>
  
  <pre><code>namespace Acme\ApiBundle\Entity;
  
  use FOS\OAuthServerBundle\Entity\Client as BaseClient;
  use Doctrine\ORM\Mapping as ORM;
  
  /**
   * @ORM\Entity
   */
  class Client extends BaseClient
  {
      /**
       * @ORM\Id
       * @ORM\Column(type="integer")
       * @ORM\GeneratedValue(strategy="AUTO")
       */
      protected $id;
  
      public function __construct()
      {
          parent::__construct();
      }
  }
  </code></pre>