def _create_user(self, username, email=None, password=None,
                     **extra_fields):
        now = timezone.now()
        email = self.normalize_email(email)
        user = self.model(username=username,
                          email=email,
                          last_login=now,
                          date_joined=now,
                          **extra_fields)
        user.set_password(password)
        user.save(using=self._db)
        return user