Refs #21379 -- Normalized unicode username inputs

tests/auth_tests/test_forms.py

@@ -3,6 +3,7 @@ from __future__ import unicode_literals
 
 import datetime
 import re
+from unittest import skipIf
 
 from django import forms
 from django.contrib.auth.forms import (
@@ -118,6 +119,28 @@ class UserCreationFormTest(TestDataMixin, TestCase):
         else:
             self.assertFalse(form.is_valid())
 
+    @skipIf(six.PY2, "Python 2 doesn't support unicode usernames by default.")
+    def test_duplicate_normalized_unicode(self):
+        """
+        To prevent almost identical usernames, visually identical but differing
+        by their unicode code points only, Unicode NFKC normalization should
+        make appear them equal to Django.
+        """
+        omega_username = 'iamtheΩ'  # U+03A9 GREEK CAPITAL LETTER OMEGA
+        ohm_username = 'iamtheΩ'  # U+2126 OHM SIGN
+        self.assertNotEqual(omega_username, ohm_username)
+        User.objects.create_user(username=omega_username, password='pwd')
+        data = {
+            'username': ohm_username,
+            'password1': 'pwd2',
+            'password2': 'pwd2',
+        }
+        form = UserCreationForm(data)
+        self.assertFalse(form.is_valid())
+        self.assertEqual(
+            form.errors['username'], ["A user with that username already exists."]
+        )
+
     @override_settings(AUTH_PASSWORD_VALIDATORS=[
         {'NAME': 'django.contrib.auth.password_validation.UserAttributeSimilarityValidator'},
         {'NAME': 'django.contrib.auth.password_validation.MinimumLengthValidator', 'OPTIONS': {