For Internet facing applications, it is quite burdensome for users to have to register at your site to obtain access. It requires them to remember yet another username and password combination. Social identity providers allow you to delegate authentication to a semi-trusted and respected entity where the user probably already has an account. {{book.project.name}} provides built-in support for the most common social networks out there, such as Google, Facebook, Twitter, Github, LinkedIn, Microsoft and StackOverflow.