Restricting registrations to paid subscribers

[kira]

Hi all! I've been hired to administrate a forum that's an adjunct to a subscription-based online service currently in development. The company wishes to restrict forum registration and viewing to paid subscribers of this online service -- sort of similar to the way the various vB sites check to see if you're a customer before allowing you to post, download and/or get support.

(At first I thought hey, we'll just password-protect the forums and give new subscribers the password in their "my account" area of the online service -- but then I realized that this wouldn't prevent smart alecks from giving out the password to friends/nonsubscribers!)

Any ideas on how this can be accomplished? A free hack would be ideal of course, but my bosses would probably accept a recommendation if something along these lines would require a paid programmer with vBulletin-expertise.

(Note that while our vb3 is on a *nix server, the online service is running on a separate ASP.NET server -- not sure if that matters but I thought I'd better mention it just in case!)

All ideas and help would be greatly appreciated. Many thanks!