For it to work at all, each user would have to have a different URL for each group they were in. Along with nearly every other SSO solution short of LDAP, Open

For it to work at all, each user would have to have a different URL for each group they were in. Along with nearly every other SSO solution short of LDAP, OpenID infuriatingly only authenticates the username — it provides no means whatsoever for context about the user, much less group membership. Brad Fitzpatrick (the creator of OpenID and founder of LiveJournal) has been working on a new protocol called WebFinger to add context to usernames, but so far they've avoided trying to codify a mechanism for group membership.