Best approach to maintain session vars across multiple domains

I am building a tool-bar like umbrella system to link four different sites together and need to log in once from any of the sites but then allow access to all the other sites. There is also a lot of data I need to maintain between sessions. What would be the best approach for this? I have already wondered about just storing session in the db and retrieving upon moving to a new site but am wondering if this is the best techniqu开发者_如何学运维e.

---

Absolutely effective method but if session variable is changed then you have to find a script which gets refresh and collects the session variable

---

Well its a very effectiv technique thats for sure. Its easy to maintain a central database accessible from everysites. And down the road they might share more information if they are at all related so thats another + to me.

See this discussion here about exactly that subject.