public static function launchCourse($idCourse, $token, $page)
 {
     $app = \Slim\Slim::getInstance();
     if (!Course::find($idCourse)) {
         $app->halt("404");
     }
     $auth = Auth_Token::where('token', '=', $token)->first();
     if (!$auth || Enrollment::where('user_id', '=', $auth->user_id)->where('course_id', '=', $idCourse)->count() == 0) {
         $app->response->headers->set('Content-Type', 'text/html');
         $app->render('course_launch_401.php');
         $app->stop();
     }
     FileController::readCourse($idCourse, $page);
 }