AUTHENTICATION_BACKENDS = ('accounts.backend.AuthBackend',)

def login(request):
if request.method == 'POST':
    username_or_email = request.POST['username']
    password = request.POST['password']
    user = authenticate(username=username_or_email, password=password)
    print(user)
    if user is not None:
        return reverse('task:home')
    else:
        messages.error(request, "Username or password is invalid")
        return render(request, 'accounts/login.html')
else:
    return render(request, 'accounts/login.html')

from django.contrib.auth.models import User
from django.db.models import Q


class AuthBackend(object):
    supports_object_permissions = True
    supports_anonymous_user = False
    supports_inactive_user = False

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

    def authenticate(self, username, password):
        print('inside custom auth')
        try:
            user = User.objects.get(
                Q(username=username) | Q(email=username) )
            print(user)
        except User.DoesNotExist:
            return None
        print(user)
        if user.check_password(password):
             return user
        else:
            return None