How do I ignore the Identity Framework magic and just use the OWIN auth middleware to get the claims I seek?

The OWIN middleware stuff to integrate third-party logins to your ASP.NET app is very cool, but I can’t seem to figure out how to tear it out from the new ID framework that replaces the crappy Membership API. I’m not interested in persisting the resulting claims and user info in that EF-based data persistence, I just want the claims info so I can apply it to my own user accounts in existing projects. I don’t want to adopt the new ID framework just to take advantage of this stuff.