openid - Single user system across multiple sites using Codeigniter and XenForo -

i've got several sites i'd have same user system for.

one of sites runs xenforo, others run codeigniter, or systems built on codeigniter (e.g pyrocms).

i need somehow able let user login on of sites same username/password combination, in addition able register.

i know there number of ways of going this, such openid server, i'm not 100% sure best situation given i'm using 2 systems arent going play nice together.

i'm not bothered having autologin across sites @ once, dont want people have use multiple different credentials.

would right in thinking along lines of central openid server, openid authentication on 'slave' sites best option?

i'd ideally use xenforo user table 'master' user table in situation.

any input or suggestions appreciated.

i wrote 1 here while ago, i've not updated in while though should still :

http://www.jeremyhutchings.com/2010/12/xenforo-and-codeigniter-intergration.html