To embed login form in a 3rd-party website, copy the following code, change "youreventname" to your event's name eg. tedx2017, and paste it into your website:
<i frame src="https://youreventname.dryfta.com/index.php?option=com_dryfta&view=register&layout=login&tmpl=component" width="100%" height="500px" allowfullscreen="" style="background: url(https://app.dryfta.com/templates/dryfta_theme/images/dryfta_loading_icon.svg) center no-repeat #fff;border:none;"></i frame>