I have joomla site running with users registered. I purchased CashbackEngine, installed at subdomain. I need that users could register with their existing joomla creditentials at this new CashbackEngine subdomain. There is no need that new users could sign-up to both sites via CashbackEngine subdomain (users would be redirected to sign up to joomla site).
The user needs to be automatically logged into the cashback site if he clicks on the link from the joomla site