From the Acegi Security mailing list:
Thanks to the efforts of Robin Bramley; we now have a first draft of OpenID support in the sandbox. The code is mostly as-is from when Robin submitted sent it to me. I've done all the standard jalopy formatting of the code so it blends in and has the proper file headers.
I don't know how much this will help folks developing intranet applications, but it's pretty cool for those doing otherwise. Anyone want to take a stab getting OpenID working with Roller? It uses Acegi and supports SSO, so hopefully it won't be too difficult.
See Timothy M. O'Brien's writeup as well as Ray Krueger's for more information.