Custom backend for case insensitive login with email address to prevent login failures for people who created their accounts on device that automatically uppercases input fields (i.e. iOS)

backends.py

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


class CustomModelBackend(ModelBackend):
    """
    Subclass the default ModelBackend
    """

    def authenticate(self, username=None, password=None, **kwargs):
        UserModel = get_user_model()
        if username is None:
            username = kwargs.get(UserModel.USERNAME_FIELD)
        try:
            # replace default lookup with case insensitive lookup by email
            # note: this presumes a CustomUser and login form that saves email to username field
            #user = UserModel._default_manager.get_by_natural_key(username)
            user = UserModel.objects.get(email__iexact=username)
            if user.check_password(password):
                return user
        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)

settings.py

# custom auth backend replaces default ModelBackend
AUTHENTICATION_BACKENDS = ('core.backends.CustomModelBackend',)