change authentication backend only for admin django code example

Example 1: django authenticate with email

from django.contrib.auth import get_user_model
from django.contrib.auth.backends import ModelBackend

class EmailBackend(ModelBackend):
    def authenticate(self, request, username=None, password=None, **kwargs):
        UserModel = get_user_model()
        try:
            user = UserModel.objects.get(email=username)
        except UserModel.DoesNotExist:
            return None
        else:
            if user.check_password(password):
                return user
        return None

Example 2: how to create staff account in django

user = User.objects.create_user('john', '[email protected]', 'johnpassword')  
user.is_staff=True 
user.save()