Django : Case insensitive matching of username from auth user?

I modified few lines in my registration and login process that seems to work for me. With my solution usernames will still be displayed like the user wrote them when registering, but it will not allow others to use the same username written differently. It also allows users to login without worrying about writing the case sensitive username.

I modified the registration form to search for case insensitive usernames.

This is line from my validation of username, it searches for user with this username.

User._default_manager.get(username__iexact=username)

Then I needed to allow users to login with case insensitive usernames.

From my login view:

username = request.POST['username']
password = request.POST['password']
caseSensitiveUsername = username
try:
  findUser = User._default_manager.get(username__iexact=username)
except User.DoesNotExist:
  findUser = None
if findUser is not None:
  caseSensitiveUsername = findUser.get_username
user = auth.authenticate(username=caseSensitiveUsername, password=password)

The simplest way to use case insensitive username is to inherit from default ModelBackend and override authenticate method.

Please note that inside the except block we are executing UserModel().set_password(password), by doing this we decreasing hasher work time. Fixed bug report

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

from users.models import User

class CaseInsensitiveModelBackend(ModelBackend):
    def authenticate(self, username=None, password=None, **kwargs):
        UserModel = get_user_model()
        if username is None:
            username = kwargs.get(UserModel.USERNAME_FIELD)
        try:
            d = {'%s__iexact'%UserModel.USERNAME_FIELD: username}
            user = UserModel.objects.get(**d)
            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)

        return None

And add this backend to AUTHENTICATION_BACKENDS in settings.py

AUTHENTICATION_BACKENDS = (
    'sdcpy.backends.CaseInsensitiveModelBackend', # inherits from 'django.contrib.auth.backends.ModelBackend'
)

As of Django 1.5, making usernames case insensitive is straightforward:

class MyUserManager(BaseUserManager):
    def get_by_natural_key(self, username):
        return self.get(username__iexact=username)

Sources: 1, 2

Finally got it :

With so much experimenting and minimum effect on User model, finally achieved it. [ Thanks to Mr. @freakish for a different thought ]

Here it is :

############ username case-insensitivity ############
class iunicode(unicode):
    def __init__(self, value):
        super(iunicode, self).__init__(value)
        self.value = value

    def __eq__(self, other):
        if isinstance(other, str) or isinstance(other, unicode):
            return self.value.lower() == other.lower()
        if isinstance(other, self.__class__):
            return other == self.value


def custom_getattribute(self, name):
    val = object.__getattribute__(self, name)
    if name == "username":
        val = iunicode(val)
    return val

def auth_user_save(self, *args, **kwargs): # Ensures lowercase usernames
    username = self.username
    if username and type(username) in [unicode, str, iunicode]:
        self.username = username.lower()   # Only lower case allowed
    super(User, self).save(*args, **kwargs)

User.__getattribute__ = custom_getattribute
User.save = MethodType(auth_user_save, None, User)
#####################################################

I tested it and it worked as expected. :D

So, here are the testcases :

from django.test.testcases import TestCase

def create_user(data='testuser'):
    email = '%s@%s.com' % (data, data)
    user = G(User, username=data, email=email, is_active=True)
    user.set_password(data)
    user.save()
    return user

class UsernameCaseInsensitiveTests(TestCase):

    def test_user_create(self):
        testuser = 'testuser'
        user = create_user(testuser)
        # Lowercase
        self.assertEqual(testuser, user.username)
        # Uppercase
        user.username = testuser.upper()
        user.save()
        self.assertEqual(testuser, user.username)

def test_username_eq(self):
    testuser = 'testuser'
    user = create_user(testuser)
    self.assertTrue(isinstance(user.username, iunicode))
    self.assertEqual(user.username, testuser)
    self.assertEqual(user.username, testuser.upper())
    self.assertTrue(user.username == testuser.upper())
    self.assertTrue(testuser.upper() == user.username)
    self.assertTrue(user.username == iunicode(testuser.upper()))

Implicit Case-insensitive queries for database

###################### QuerySet #############################
def _filter_or_exclude(self, negate, *args, **kwargs):
    if 'username' in kwargs:
        kwargs['username__iexact'] = kwargs['username']
        del kwargs['username']
    if args or kwargs:
        assert self.query.can_filter(),\
        "Cannot filter a query once a slice has been taken."
    from django.db.models import Q
    clone = self._clone()
    if negate:
        clone.query.add_q(~Q(*args, **kwargs))
    else:
        clone.query.add_q(Q(*args, **kwargs))
    return clone

from django.db.models.query import QuerySet
QuerySet._filter_or_exclude = _filter_or_exclude
#############################################################

This will allow, User.objects.get(username='yugal') & User.objects.get(username='YUGAl') yield the same user.