如何让用户在Django social-auth注册时设置用户名?

I use Django social-auth (omab version just to avoid any confusion with the other similarly named project) and right now I am trying it with Facebook. It is possible to register a new user and to login/logout without any issue. The only thing that I would like to add is a form during registration to let the user enter the desired username to be used on site because at the moment the username is either a facebook username (I do not want to force the user to use the same username) or a uuid if there is no facebook username (and that is ugly).I use Django social-auth (omab version just to