def __init__(self, request=None, *args, **kwargs):
        self.request = request
        self.user_cache = None
        super(AuthenticationForm, self).__init__(*args, **kwargs)
If request is passed in, the form will validate that cookies are
dataset/ETHPy150Open AppScale/appscale/AppServer/lib/django-1.4/django/contrib/auth/forms.py/AuthenticationForm.__init__