With thanks for contributions from John and Damir, Authlogic_RPX 1.1.1 is now available and includes an internal identity mapping that lets you tie multiple authentication methods to a single user. There are also some other bug fixes and improvements, so it is recommended you update Authlogic_RPX even if you don't want to enable the identity mapping.
See the Authlogic_RPX repo on github for information about installation, usage, and don't forget the sample site (and sample code).
Under the covers, it uses the RPX service from JanRain, a bit like this:
To get a better idea of why you might want to use Authlogic_RPX, and some pointers on how to do it, here's a reprise of my presentation on the subject to the singapore Ruby Brigade last year:
Rails authentication with Authlogic RPX
View more presentations from Paul Gallagher.
Soundtrack for this post? (I want) Security Jo Jo Zep & The Falcons. 1977, tight pants, mo and all;-)