Using Loginsession Cross Domain With Opencart

Hi All.

I need to have a webshop with my site. And it just seems like a waste to write one myself. First of all, it will not be as great as a OpenCart. And secondly its gonna take hundreds of hours.

So i've got my Yii-app in domain.com, and I have a OpenCart installation in webshop.domain.com.
But I cant ask my users to register accounts both in the shop and in my community-site.

So if i write my yii-app to use the OC-user database, I need the possibility to auth on any of the sites, then seemlessly jump between them without the need for re-authentication.

Can anyone point me to a tutorial or any writings on this topic? And, is this a good idea? Any comments or suggestions?

Thank you.