http://chriskief.com/2012/12/18/django-modelform-formview-and-the-request-object/

forms.py

class RegisterForm(forms.ModelForm):

    username = forms.CharField(max_length=User._meta.get_field('username').max_length)
    email = forms.CharField(max_length=User._meta.get_field('email').max_length, widget=HTML5EmailInput())
    password = forms.CharField(min_length=6, max_length=16, widget=forms.PasswordInput())

    # the request is now available, add it to the instance data
    def __init__(self, *args, **kwargs):
        self.request = kwargs.pop('request')
        super(RegisterForm, self).__init__(*args, **kwargs)