public function tenants($token = NULL) {
    $url = $this->url() . '/tenants';

    if (empty($token)) {
      $token = $this->token();
    }

    $headers = array(
      'X-Auth-Token' => $token,
      'Accept' => 'application/json',
      //'Content-Type' => 'application/json',
    );

    $client = \HPCloud\Transport::instance();
    $response = $client->doRequest($url, 'GET', $headers);

    $raw = $response->content();
    $json = json_decode($raw, TRUE);

    return $json['tenants'];

  }