function prepareResponse($endform=false) {
        $return_url = $this->returnUrl();
        $parms = $this->getContentItemSelection();
        $parms = LTIX::signParameters($parms, $return_url, "POST", "Install Content");
        $endform = '<a href="index.php" class="btn btn-warning">Back to Store</a>';
        $content = LTI::postLaunchHTML($parms, $return_url, true, false, $endform);
        return $content;
    }