Fixed #17869 - force logout when REMOTE_USER header disappears

If the current sessions user was logged in via a remote user backend log out
the user if REMOTE_USER header not available - otherwise leave it to other auth
middleware to install the AnonymousUser.

Thanks to Sylvain Bouchard for the initial patch and ticket maintenance.

django/contrib/auth/middleware.py

 from django.contrib import auth
+from django.contrib.auth import load_backend
+from django.contrib.auth.backends import RemoteUserBackend
 from django.core.exceptions import ImproperlyConfigured
 from django.utils.functional import SimpleLazyObject
 
@@ -47,9 +49,18 @@ class RemoteUserMiddleware(object):
         try:
             username = request.META[self.header]
         except KeyError:
-            # If specified header doesn't exist then return (leaving
-            # request.user set to AnonymousUser by the
-            # AuthenticationMiddleware).
+            # If specified header doesn't exist then remove any existing
+            # authenticated remote-user, or return (leaving request.user set to
+            # AnonymousUser by the AuthenticationMiddleware).
+            if request.user.is_authenticated():
+                try:
+                    stored_backend = load_backend(request.session.get(
+                        auth.BACKEND_SESSION_KEY, ''))
+                    if isinstance(stored_backend, RemoteUserBackend):
+                        auth.logout(request)
+                except ImproperlyConfigured as e:
+                    # backend failed to load
+                    auth.logout(request)
             return
         # If the user is already authenticated and that user is the user we are
         # getting passed in the headers, then the correct user is already

django/contrib/auth/tests/remote_user.py

 from datetime import datetime
 
 from django.conf import settings
+from django.contrib.auth import authenticate
 from django.contrib.auth.backends import RemoteUserBackend
-from django.contrib.auth.models import User
+from django.contrib.auth.models import User, AnonymousUser
 from django.contrib.auth.tests.utils import skipIfCustomUser
 from django.test import TestCase
 from django.utils import timezone
@@ -23,7 +24,7 @@ class RemoteUserTest(TestCase):
         self.curr_middleware = settings.MIDDLEWARE_CLASSES
         self.curr_auth = settings.AUTHENTICATION_BACKENDS
         settings.MIDDLEWARE_CLASSES += (self.middleware,)
-        settings.AUTHENTICATION_BACKENDS = (self.backend,)
+        settings.AUTHENTICATION_BACKENDS += (self.backend,)
 
     def test_no_remote_user(self):
         """
@@ -97,6 +98,26 @@ class RemoteUserTest(TestCase):
         response = self.client.get('/remote_user/', REMOTE_USER=self.known_user)
         self.assertEqual(default_login, response.context['user'].last_login)
 
+    def test_header_disappears(self):
+        """
+        Tests that a logged in user is logged out automatically when
+        the REMOTE_USER header disappears during the same browser session.
+        """
+        User.objects.create(username='knownuser')
+        # Known user authenticates
+        response = self.client.get('/remote_user/', REMOTE_USER=self.known_user)
+        self.assertEqual(response.context['user'].username, 'knownuser')
+        # During the session, the REMOTE_USER header disappears. Should trigger logout.
+        response = self.client.get('/remote_user/')
+        self.assertEqual(response.context['user'].is_anonymous(), True)
+        # verify the remoteuser middleware will not remove a user
+        # authenticated via another backend
+        User.objects.create_user(username='modeluser', password='foo')
+        self.client.login(username='modeluser', password='foo')
+        authenticate(username='modeluser', password='foo')
+        response = self.client.get('/remote_user/')
+        self.assertEqual(response.context['user'].username, 'modeluser')
+
     def tearDown(self):
         """Restores settings to avoid breaking other tests."""
         settings.MIDDLEWARE_CLASSES = self.curr_middleware

docs/releases/1.5.txt

@@ -296,6 +296,9 @@ Django 1.5 also includes several smaller improvements worth noting:
   you to test equality for XML content at a semantic level, without caring for
   syntax differences (spaces, attribute order, etc.).
 
+* RemoteUserMiddleware now forces logout when the REMOTE_USER header
+  disappears during the same browser session.
+
 Backwards incompatible changes in 1.5
 =====================================