I'm trying to integrate my blog's commenting system with an existing user database.

In the TypeKey FAQ, it says

QUOTE
Is it possible to use an alternate sign-on system for Movable Type or other tools?

Yes. There are a number of TypeKey-compatible third-party authentication systems available. These can run as your own local user database or as a front-end for existing login systems.

But I' ve looked and I haven't seen anything that does this. Are there any resources online, or folks who have done this before that might be able to assist me?

TTFN
Travis