See: http://microformats.org/wiki/relmeauth for more details.
http://microformats.org/wiki/RelMeAuth is nifty... like OpenId but even simpler.
RelMeAuth looks good, might have to re-add rel=me's to my site http://microformats.org/wiki/RelMeAuth
Invited to @IndieWebCamp, didn't have IndieAuth domain to login. Took 10s to add rel="me" to homepage. No "providers". Your move OpenID
Open source implementations
Q: Why does RelMeAuth need a silo backlink?
There are also usability, error detection, and recovery reasons for keeping such a double opt-in mechanism when delegating authentication. For example, it prevents one from delegating their RelMeAuth to another person's silo account.