I'm in the process of developing an IPB Integration package for Fuel. Sure there is IPBWI, but that's bulky. It loads in the IPB core which really is a pain to deal with. My integration package does not use the core. Currently their isn't much to it, and I haven't written any docs or anything yet.
Basically you load the package manually or automatically, then preferably in your base controllers before() method or anywhere really, call IPB::factory()
The factory method sets up a few things, and will detect if a user is logged in or not.
You can then fetch user details with: IPB::user()->member_id
That will give you the members ID. Some other methods you can use are:
IPB_Member::is_logged() - Returns true/false depending on users logged in status.
IPB_Member::is_group() - Can take group ids or group names (as set in the config), eg: IPB_Member::is_group('Administrators','Members','Validating')
IPB_Member::has_permission() - Determines if user has said permission, eg: IPB_Member::has_permission('g_is_supmod')
Then of course...
IPB_Auth::login() and IPB_Auth::logout()
For now there isn't too much functionality, just the basics. I plan on making it a lot better as I use it for my own site. It won't have everything IPBWI has because there is just too much that relies heavily on the IPB core, I will however try to get most things.
You can snag it via GitHub from here: https://github.com/jaysonic/IPB-Fuel-Integration
I'll keep this thread updated with the fixes/changes/releases.
Any requests, bugs, tips or feedback is appreciated.
Update: You can see the development branch here.