docs: def clean(self):
          """
          Authenticate the given username/email and password. If the fields
          are valid, store the authenticated user for returning via save().
          """
          username = self.cleaned_data.get("username")
          password = self.cleaned_data.get("password")
          self._user = authenticate(username=username, password=password)
          if self._user is None:
              raise forms.ValidationError(
                               ugettext("Invalid username/email and password"))
          elif not self._user.is_active:
              raise forms.ValidationError(ugettext("Your account is inactive"))
          return self.cleaned_data