EmailOrUsernameModelBackend - Django authentication backend for logging in using either username or email address

backend.py

from django.contrib.auth.models import User


class EmailOrUsernameModelBackend(object):
    """
    Custom authentication backend against django.contrib.auth.models.User that
    allows logging in using either username or email address. Intended to be
    used in conjunction with django.contrib.auth.backends.ModelBackend.
    """

    def authenticate(self, username=None, password=None):
        if '@' in username:
            kwargs = {'email': username}
        else:
            kwargs = {'username': username}
        try:
            user = User.objects.get(**kwargs)
            if user.check_password(password):
                return user
        except User.DoesNotExist:
            return None

    def get_user(self, user_id):
        try:
            return User.objects.get(pk=user_id)
        except User.DoesNotExist:
            return None

Why this is not working

Try this:
In your settings.py file add:
AUTHENTICATION_BACKENDS = ['authentication.views.EmailOrUsernameModelBackend']

In my case i have authentication app and inside this app i have views.py where i wrote this above class, and don't forgot to replace (object) as ModelBackend. This can surely help you