protected function showThankyou(LtiLaunchData $launchData)
    {
        if (!$launchData->hasReturnUrl()) {
            return true;
        }

        if ($launchData->hasVariable(DeliveryTool::PARAM_SKIP_THANKYOU)) {
            switch ($launchData->getVariable(DeliveryTool::PARAM_SKIP_THANKYOU)) {
                case 'true':
                    return false;
                case 'false':
                    return true;
                default:
                    $this->logWarning('Unexpected value for \''.DeliveryTool::PARAM_SKIP_THANKYOU.'\': '
                        .$launchData->getVariable(DeliveryTool::PARAM_SKIP_THANKYOU));
            }
        }
        return $this->getOption(self::OPTION_THANK_YOU_SCREEN);
    }