Fixed #36717 -- Redirect authenticated users on admin login view to next URL.

Co-authored-by: Natalia <124304+nessita@users.noreply.github.com>

AUTHORS

@@ -159,6 +159,7 @@ answer newbie questions, and generally made Django that much better:
     Ben Slavin <benjamin.slavin@gmail.com>
     Ben Sturmfels <ben@sturm.com.au>
     Bendegúz Csirmaz <csirmazbendeguz@gmail.com>
+    Benedict Etzel <developer@beheh.de>
     Berker Peksag <berker.peksag@gmail.com>
     Bernd Schlapsi
     Bernhard Essl <me@bernhardessl.com>

django/contrib/admin/sites.py

@@ -416,29 +416,27 @@ class AdminSite:
         """
         Display the login form for the given HttpRequest.
         """
-        if request.method == "GET" and self.has_permission(request):
-            # Already logged-in, redirect to admin index
-            index_path = reverse("admin:index", current_app=self.name)
-            return HttpResponseRedirect(index_path)
-
         # Since this module gets imported in the application's root package,
         # it cannot import models from other applications at the module level,
         # and django.contrib.admin.forms eventually imports User.
         from django.contrib.admin.forms import AdminAuthenticationForm
         from django.contrib.auth.views import LoginView
 
+        redirect_url = LoginView().get_redirect_url(request) or reverse(
+            "admin:index", current_app=self.name
+        )
+        if request.method == "GET" and self.has_permission(request):
+            # Already logged-in, redirect accordingly.
+            return HttpResponseRedirect(redirect_url)
+
         context = {
             **self.each_context(request),
             "title": _("Log in"),
             "subtitle": None,
             "app_path": request.get_full_path(),
             "username": request.user.get_username(),
+            REDIRECT_FIELD_NAME: redirect_url,
         }
-        if (
-            REDIRECT_FIELD_NAME not in request.GET
-            and REDIRECT_FIELD_NAME not in request.POST
-        ):
-            context[REDIRECT_FIELD_NAME] = reverse("admin:index", current_app=self.name)
         context.update(extra_context or {})
 
         defaults = {

django/contrib/auth/views.py

@@ -40,20 +40,28 @@ class RedirectURLMixin:
     def get_success_url(self):
         return self.get_redirect_url() or self.get_default_redirect_url()
 
-    def get_redirect_url(self):
-        """Return the user-originating redirect URL if it's safe."""
-        redirect_to = self.request.POST.get(
-            self.redirect_field_name, self.request.GET.get(self.redirect_field_name)
+    def get_redirect_url(self, request=None):
+        """Return the user-originating redirect URL if it's safe.
+
+        Optionally takes a request argument, allowing use outside class-based
+        views.
+        """
+        if request is None:
+            request = self.request
+        redirect_to = request.POST.get(
+            self.redirect_field_name, request.GET.get(self.redirect_field_name)
         )
         url_is_safe = url_has_allowed_host_and_scheme(
             url=redirect_to,
-            allowed_hosts=self.get_success_url_allowed_hosts(),
-            require_https=self.request.is_secure(),
+            allowed_hosts=self.get_success_url_allowed_hosts(request),
+            require_https=request.is_secure(),
         )
         return redirect_to if url_is_safe else ""
 
-    def get_success_url_allowed_hosts(self):
-        return {self.request.get_host(), *self.success_url_allowed_hosts}
+    def get_success_url_allowed_hosts(self, request=None):
+        if request is None:
+            request = self.request
+        return {request.get_host(), *self.success_url_allowed_hosts}
 
     def get_default_redirect_url(self):
         """Return the default redirect URL."""

docs/releases/6.1.txt

@@ -92,7 +92,8 @@ Minor features
 :mod:`django.contrib.admin`
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-* ...
+* The admin site login view now redirects authenticated users to the next URL,
+  if available, instead of always redirecting to the admin index page.
 
 :mod:`django.contrib.admindocs`
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

tests/admin_views/tests.py

@@ -2413,6 +2413,32 @@ class AdminViewPermissionsTest(TestCase):
         self.assertEqual(response.status_code, 200)
         self.assertEqual(response.context[REDIRECT_FIELD_NAME], reverse("admin:index"))
 
+    def test_login_redirect_when_logged_in(self):
+        self.client.force_login(self.superuser)
+        response = self.client.get(reverse("admin:login"))
+        self.assertRedirects(response, reverse("admin:index"))
+
+    def test_login_redirect_to_next_url_when_logged_in(self):
+        self.client.force_login(self.superuser)
+        next_url = reverse("admin:admin_views_article_add")
+        response = self.client.get(
+            reverse("admin:login"),
+            query_params={REDIRECT_FIELD_NAME: next_url},
+        )
+        self.assertRedirects(response, next_url)
+
+    def test_login_redirect_unsafe_next_url_when_logged_in(self):
+        self.client.force_login(self.superuser)
+        response = self.client.get(
+            reverse("admin:login"),
+            query_params={
+                REDIRECT_FIELD_NAME: "https://example.com/bad",
+            },
+        )
+        self.assertRedirects(
+            response, reverse("admin:index"), fetch_redirect_response=False
+        )
+
     def test_login_has_permission(self):
         # Regular User should not be able to login.
         response = self.client.get(reverse("has_permission_admin:index"))