http://www.sitepoint.com/series/using-social-networks-as-a-login-system/
Every part of the article has a seperate branch, except part 3, allowing you to easily follow the serie.
Setup: part1
Google+: part2
Twitter: part4
Facebook: part4
peternijssen/sitepoint-social-login
Git repository with the code of my Social Login series on SitePoint