I have a site that I currently have up and running built in wordpress. I'm looking to integrate a forum within it. I'd prefer an external authenticator across both (OAuth or similar?) so that an update to Wordpress' authentication protocols would not necessarily break it in the future. I own a vBulletin [url removed, login to view] license.
* Users only log in once, on my forums homepage or in the entire sites header in any page.
* Users (regular users, writers, admins,e tc.) have access to their Wordpress profile/back-end as necessary.
That's it. Should be rather easy IMO.