/**
  * Retrieve the response object for when authentication is missing.
  *
  * @since 1.0
  *
  * @param Authenticatable $endpoint
  *
  * @return Response
  */
 protected function generate_auth_missing(Authenticatable $endpoint)
 {
     $response = new Response(array('success' => false, 'error' => array('code' => $endpoint->get_auth_error_code(), 'message' => $endpoint->get_auth_error_message())), 401);
     switch ($endpoint->get_auth_mode()) {
         case Authenticatable::MODE_VALID_ACTIVATION:
             $realm = __("An active license key is required to access this resource, passed as the username, and the activation record ID as the password.", Plugin::SLUG);
             break;
         case Authenticatable::MODE_ACTIVE:
             $realm = __("An active license key is required to access this resource, passed as the username. Leave password blank.", Plugin::SLUG);
             break;
         case Authenticatable::MODE_EXISTS:
         default:
             $realm = __("A license key is required to access this resource, passed as the username. Leave password blank.", Plugin::SLUG);
             break;
     }
     $response->header('WWW-Authenticate', "Basic realm=\"{$realm}\"");
     return $response;
 }