OpenID is a wonderful concept. If I visit a web site, Acme Widgets, I only need to supply a URL that belongs to me in order to log in. The web site at that URL will provide a place where I can authorize Acme Widgets to log me in with this id.
The benefit of this type of identity system is now you don’t need to create new username’s and passwords for each site you’d like to use. We initially began reviewsby.us with just OpenID for that reason. Now we can target places like livejournal and make it exceptionally easy for their users to register with our site.
As of this writing, and even more robust system is being developed, whobar. Whobar supports multiple identification sites, not just OpenID. Rather than walking through explaining how to do a sign-in system that integrates OpenID, I’ll direct people to whobar. It is in the plans for reviewsby.us to integrate whobar and once that happens you can expect a shiny tutorial and/or plugin for symfony.