fix(api): enforce POST on SAML ACS endpoint (#12393)

api/changelog.d/saml-acs-post-only.fixed.md

@@ -0,0 +1 @@
+`/api/v1/accounts/saml/{organization_slug}/acs/` rejects non-POST requests before SAML response processing

api/src/backend/api/tests/test_views.py

@@ -14673,6 +14673,37 @@ class TestSAMLConfigurationViewSet:
         assert not SAMLConfiguration.objects.filter(id=config.id).exists()
 
 
+@pytest.mark.django_db
+class TestSAMLACSView:
+    def test_get_is_not_allowed(self, client, saml_setup):
+        response = client.get(
+            reverse(
+                "saml_acs",
+                kwargs={"organization_slug": saml_setup["domain"]},
+            )
+        )
+
+        assert response.status_code == status.HTTP_405_METHOD_NOT_ALLOWED
+        assert response.headers["Allow"] == "POST"
+        assert "saml-acs-session" not in response.cookies
+
+    def test_post_is_forwarded_to_allauth(self, client, saml_setup):
+        response = client.post(
+            reverse(
+                "saml_acs",
+                kwargs={"organization_slug": saml_setup["domain"]},
+            ),
+            data={"SAMLResponse": "test-saml-response"},
+        )
+
+        assert response.status_code == status.HTTP_302_FOUND
+        assert response.url == reverse(
+            "saml_finish_acs",
+            kwargs={"organization_slug": saml_setup["domain"]},
+        )
+        assert "saml-acs-session" in response.cookies
+
+
 @pytest.mark.django_db
 class TestTenantFinishACSView:
     def test_dispatch_skips_if_user_not_authenticated(self, monkeypatch):

api/src/backend/api/v1/urls.py

@@ -46,6 +46,7 @@ from api.v1.views import (
 from django.http import JsonResponse
 from django.urls import include, path
 from django.views.decorators.csrf import csrf_exempt
+from django.views.decorators.http import require_POST
 from drf_spectacular.views import SpectacularRedocView
 from rest_framework_nested import routers
 
@@ -194,7 +195,7 @@ urlpatterns = [
     ),
     path(
         "accounts/saml/<organization_slug>/acs/",
-        ACSView.as_view(),
+        require_POST(ACSView.as_view()),
         name="saml_acs",
     ),
     path(