I have lately tried the qa-open-login plugin to give users the option signing up with twitter. It does work just fine ( by the way many thanks to Alex Lixandru.).
The upside of this plugin ( twitter as provider) is that it allows you to lower the user signup friction and filling automatically the user profile (bio,pic, location, handle name) wich is fine,
The down side of it is that you can't retreive user email as twitter don't allow it. They said you have to ask users for it. Giving the fact that user email is very important in q2a, has anyone tried to enhance the plugin by adding the step of asking users their email ?