Can I share user session or cookie between two entirely different websites. I have two websites www.xxx.com and www.yyy.com(different wp installation). While logged user clicks on a link page from website1 could be redirect to website2 post details page. So user should post a comment as user.

Is this possible in entirely two different hosted websites ? (Most Preferred)

(or)

Should I do any modification like multi-site or sub domain installation.

Please suggest me your ideas on this feature.