Allow importing the backend without loading apps

Make it possible to monkey-patch the backend from the settings.

django_auth_ldap/backend.py

@@ -51,7 +51,6 @@
 import django.dispatch
 import ldap
 from django.contrib.auth import get_user_model
-from django.contrib.auth.models import Group, Permission
 from django.core.cache import cache
 from django.core.exceptions import ImproperlyConfigured, ObjectDoesNotExist
 
@@ -777,6 +776,8 @@ def _mirror_groups(self):
         Mirrors the user's LDAP groups in the Django database and updates the
         user's membership.
         """
+        from django.contrib.auth.models import Group
+
         try:
             target_group_names = frozenset(self._get_groups().get_group_names())
         except ldap.LDAPError as e:
@@ -833,6 +834,8 @@ def _load_group_permissions(self):
         Populates self._group_permissions based on LDAP group membership and
         Django group permissions.
         """
+        from django.contrib.auth.models import Permission
+
         group_names = self._get_groups().get_group_names()
 
         perms = Permission.objects.filter(group__name__in=group_names)

tests/import_test_without_django.py

@@ -0,0 +1,16 @@
+import os
+from unittest import TestCase
+
+
+class TestLoading(TestCase):
+    def test_django_not_ready(self):
+        orig_env = os.environ.copy()
+
+        def reset_env():
+            os.environ = orig_env
+
+        self.addCleanup(reset_env)
+
+        os.environ["DJANGO_SETTINGS_MODULE"] = "tests.settings"
+
+        import django_auth_ldap.backend  # noqa: F401

tox.ini

@@ -17,7 +17,9 @@ python =
     3.13 = django{42,50,51,main}
 
 [testenv]
-commands = {envpython} -Wa -b -m django test --settings tests.settings
+commands =
+    {envpython} -Wa -b -m django test --settings tests.settings
+    {envpython} -Wa -b -m unittest discover --pattern *_test_without_django.py
 deps =
     django42: Django>=4.2,<4.3
     django50: Django>=5.0,<5.1