text: from django.contrib.auth import get_user_model
  from django.contrib.auth.backends import ModelBackend
  
  
  class CaseInsensitiveEmailBackend(ModelBackend):
      def authenticate(self, request, username=None, password=None, **kwargs):
          UserModel = get_user_model()
          if username is None:
              username = kwargs.get(UserModel.USERNAME_FIELD)
  
          username_field = UserModel.USERNAME_FIELD + '__iexact'
          try:
              user = UserModel.objects.get(**{username_field: username})
          except UserModel.DoesNotExist:
              # Run the default password hasher once to reduce the timing
              # difference between an existing and a non-existing user (#20760).
              UserModel().set_password(password)
          else:
              if user.check_password(password) and self.user_can_authenticate(user):
                  return user
  