title: django social auth registration facebook email
body: <p>Hello I'd like to allow users to login/register through facebook. 
  Authentication works but backend creates User instance with the combination of first and last name (from Facebook) as a username and no email.
  Google oauth2 backend works just fine.</p>
  
  <p>Here are my settings:</p>
  
  <pre><code>  FACEBOOK_APP_ID                   = 'appid'
    FACEBOOK_API_SECRET               = 'apisecret'
    FACEBOOK_EXTENDED_PERMISSIONS = ['email']
  
    SOCIAL_AUTH_CREATE_USERS          = True
    SOCIAL_AUTH_FORCE_RANDOM_USERNAME = False
    SOCIAL_AUTH_DEFAULT_USERNAME      = 'socialauth_user'
    SOCIAL_AUTH_COMPLETE_URL_NAME     = 'socialauth_complete'
    SOCIAL_AUTH_ASSOCIATE_URL_NAME = 'socialauth_associate_complete'
    LOGIN_ERROR_URL                   = '/login/error/'
    LOGIN_REDIRECT_URL                = '/'
    SOCIAL_AUTH_USER_MODEL            = 'users.User'
    SESSION_SERIALIZER =   django.contrib.sessions.serializers.PickleSerializer'
  </code></pre>
  
  <p>My app should create users with email filled with data(email) from facebook.
  I can't overcome this.
  Can anyone help?</p>