[fix] Support phone numbers with leading zero in auth backend

This fix allows users of countries which use
leading zeros in their national phone numbers
to authenticate successfully by using the version
of their number with the leading zero, which
without this patch fails to be recognized.

README.rst

@@ -606,7 +606,7 @@ Create User
 
     POST /api/v1/users/user/
 
-**Note**: Passing ``true`` to the optional  
+**Note**: Passing ``true`` to the optional
 ``is_verified`` field allows creating users with
 their email address flagged as verified. This will
 also skip sending the verification link to their
@@ -803,27 +803,30 @@ Usage example:
 Authentication Backend
 ----------------------
 
-The authentication backend in ``openwisp_users.backends.UsersAuthenticationBackend``
-allows users to authenticate using their
-``email`` or ``phone_number`` instead of their ``username``.
-Authenticating with the ``username`` is still allowed,
-but ``email`` has precedence.
+The authentication backend in
+``openwisp_users.backends.UsersAuthenticationBackend``
+allows users to authenticate using their ``email`` or ``phone_number``
+instead of their ``username``. Authenticating with the ``username`` is
+still supported, but ``email`` takes precedence.
 
-If the username string passed is parsed as a valid phone number, then
-``phone_number`` has precedence.
+If the provided username string is parsed as a valid phone number, then
+``phone_number`` takes precedence.
 
-Phone numbers are parsed using the ``phonenumbers`` library, which means
-that even if the user adds characters like spaces, dots or dashes, the number
-will be recognized anyway.
+Phone numbers are parsed using the
+`phonenumbers <https://github.com/daviddrysdale/python-phonenumbers>`_
+library, which ensures that numbers are recognized even if users
+include characters like spaces, dots, or dashes.
 
-When parsing phone numbers, the
-`OPENWISP_USERS_AUTH_BACKEND_AUTO_PREFIXES
-<#openwisp_users_auth_backend_auto_prefixes>`_
-setting allows to specify a list of international prefixes that can
-be prepended to the username string automatically in order to allow
-users to log in without having to type the international prefix.
+The ``OPENWISP_USERS_AUTH_BACKEND_AUTO_PREFIXES`` setting allows specifying
+a list of international prefixes that can be automatically prepended to the
+username string, enabling users to log in without typing the international
+prefix.
 
-The authentication backend can also be used as follows:
+Additionally, the backend supports phone numbers with a leading zero, which
+is common in some countries for local numbers. This ensures users can
+authenticate successfully even if they include the leading zero.
+
+The authentication backend can also be used programmatically, for example:
 
 .. code-block:: python
 

openwisp_users/backends.py

@@ -11,31 +11,31 @@
 
 class UsersAuthenticationBackend(ModelBackend):
     def authenticate(self, request, username=None, password=None, **kwargs):
-        queryset = self.get_users(username)
-        try:
-            # can not use queryset.first() because it orders the queryset
-            # by pk before returning the first object which is not what we want
-            user = queryset[0]
-        except IndexError:
-            return None
-        if user.check_password(password) and self.user_can_authenticate(user):
-            return user
+        for user in self.get_users(username):
+            if user.check_password(password) and self.user_can_authenticate(user):
+                return user
 
     def get_users(self, identifier):
         conditions = Q(email=identifier) | Q(username=identifier)
         # if the identifier is a phone number, use the phone number as primary condition
-        phone_number = self._get_phone_number(identifier)
-        if phone_number:
+        for phone_number in self._get_phone_numbers(identifier):
             conditions = Q(phone_number=phone_number) | conditions
         return User.objects.filter(conditions)
 
-    def _get_phone_number(self, identifier):
+    def _get_phone_numbers(self, identifier):
         prefixes = [''] + list(app_settings.AUTH_BACKEND_AUTO_PREFIXES)
+        numbers = [identifier]
+        found = []
+        # support those countries which use
+        # leading zeros for their local numbers
+        if str(identifier).startswith('0'):
+            numbers.append(identifier[1:])
         for prefix in prefixes:
-            value = f'{prefix}{identifier}'
-            try:
-                phonenumbers.parse(value)
-                return value
-            except NumberParseException:
-                pass
-        return False
+            for number in numbers:
+                value = f'{prefix}{number}'
+                try:
+                    phonenumbers.parse(value)
+                    found.append(value)
+                except NumberParseException:
+                    continue
+        return found

openwisp_users/tests/test_backends.py

@@ -141,6 +141,10 @@ def test_partial_phone_number(self):
         self.assertEqual(auth_backend.get_users('3665243702').count(), 1)
         self.assertEqual(auth_backend.get_users('3665243702').first(), user1)
 
+        with self.subTest('test with leading zero'):
+            self.assertEqual(auth_backend.get_users('03665243702').count(), 1)
+            self.assertEqual(auth_backend.get_users('03665243702').first(), user1)
+
         with self.subTest('test different prefix which is not enabled'):
             self._create_user(
                 username='tester2',