public function getToken() {
    $cid = 'acm_payment:braintree_token';
    $token = NULL;

    if ($cache = \Drupal::cache()->get($cid)) {
      $token = $cache->data;
    }
    else {
      $token = \Drupal::service('acm.api')->getPaymentToken('braintree');
      \Drupal::cache()->set($cid, $token);
    }

    return $token;
  }