In Java world, Acegi is a powerful security framework based on Spring that allows you to simply manage authentication and authorization. AFAIU, it supports OpenID, and Facebook Connect, LDAP, NTLM, Kerberos, etc. via Grails. If you are interested how it works, take a look at diagrams in this tutorial
Anyway, this is all cool, but I'm developing a PHP application (using CodeIgniter, FWIW) and I'm looking for something similar for PHP?