Single Sign On?

[MikeTodd]

How easy/tough is it to do a single sign on system with vBulletin? Having worked with SMF and phpBB before, it's dead simple with those, but everything I've researched for vBulletin makes it seem like this is very complex. I'm hoping that's wrong though.

Here's what I'm wanting to do: I have a custom-coded chat community site that currently uses phpBB as the forum, and login database. The rest of the site uses the forum's login system, by using a simple include to see if someone is logged into the forum and using the forum's user data if so. In phpBB the code is a little longer, but with SMF the code is a one-line include to do this.

Does something similar exist with vBulletin? I love vBulletin in general, and would be more than willing to buy a license for it, but this is a must-have for my site. (Also on my wishlist would be a plugin install/upgrade system, Wordpress has.)