From 3df3c5e67070949887e08282a332cc34c1f05184 Mon Sep 17 00:00:00 2001
From: Baptiste Mispelon <bmispelon@gmail.com>
Date: Mon, 9 Dec 2019 17:50:28 +0100
Subject: [PATCH] Fixed #26480 -- Fixed crash of contrib.auth.authenticate() on
 decorated authenticate() methods of authentication backends.

The Signature API (PEP 362) has better support for decorated functions
(by default, it follows the __wrapped__ attribute set by
functools.wraps for example).
---
 django/contrib/auth/__init__.py        |  3 ++-
 tests/auth_tests/test_auth_backends.py | 14 ++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/django/contrib/auth/__init__.py b/django/contrib/auth/__init__.py
index 6d99aa0c9b..09db690b5c 100644
--- a/django/contrib/auth/__init__.py
+++ b/django/contrib/auth/__init__.py
@@ -63,8 +63,9 @@ def authenticate(request=None, **credentials):
     If the given credentials are valid, return a User object.
     """
     for backend, backend_path in _get_backends(return_tuples=True):
+        backend_signature = inspect.signature(backend.authenticate)
         try:
-            inspect.getcallargs(backend.authenticate, request, **credentials)
+            backend_signature.bind(request, **credentials)
         except TypeError:
             # This backend doesn't accept these credentials as arguments. Try the next one.
             continue
diff --git a/tests/auth_tests/test_auth_backends.py b/tests/auth_tests/test_auth_backends.py
index 92c60af7d6..b6aa1a2833 100644
--- a/tests/auth_tests/test_auth_backends.py
+++ b/tests/auth_tests/test_auth_backends.py
@@ -13,6 +13,7 @@ from django.http import HttpRequest
 from django.test import (
     SimpleTestCase, TestCase, modify_settings, override_settings,
 )
+from django.views.decorators.debug import sensitive_variables
 
 from .models import (
     CustomPermissionsUser, CustomUser, CustomUserWithoutIsActiveField,
@@ -642,6 +643,12 @@ class SkippedBackend:
         pass
 
 
+class SkippedBackendWithDecoratedMethod:
+    @sensitive_variables()
+    def authenticate(self):
+        pass
+
+
 class AuthenticateTests(TestCase):
     @classmethod
     def setUpTestData(cls):
@@ -664,6 +671,13 @@ class AuthenticateTests(TestCase):
         """
         self.assertEqual(authenticate(username='test', password='test'), self.user1)
 
+    @override_settings(AUTHENTICATION_BACKENDS=(
+        'auth_tests.test_auth_backends.SkippedBackendWithDecoratedMethod',
+        'django.contrib.auth.backends.ModelBackend',
+    ))
+    def test_skips_backends_with_decorated_method(self):
+        self.assertEqual(authenticate(username='test', password='test'), self.user1)
+
 
 class ImproperlyConfiguredUserModelTest(TestCase):
     """