[eluser]coldclimate[/eluser]
The elephant in the room it probably querystrings. I don't know if they're just common practice in oAuth authentication, or actually a requirement in the standard, but CI doesn't handle them easily (and please don't chime in with why/for/against again, it's been done to death).
If I can't find anything suitable this week I might bite the bullet and develop. Maybe. If I can face the pain.