core: fix source_flow_manager throwing error when authenticated user attempts to re-authenticate with existing link

authentik/core/sources/flow_manager.py

@@ -129,6 +129,11 @@
             )
             new_connection.user = self.request.user
             new_connection = self.update_user_connection(new_connection, **kwargs)
+            if existing := self.user_connection_type.objects.filter(
+                source=self.source, identifier=self.identifier
+            ).first():
+                existing = self.update_user_connection(existing)
+                return Action.AUTH, existing
             return Action.LINK, new_connection
 
         action, connection = self.matcher.get_user_action(self.identifier, self.user_properties)

authentik/core/tests/test_source_flow_manager.py

@@ -81,6 +81,22 @@
             reverse("authentik_core:if-user") + "#/settings;page-sources",
         )
 
+    def test_authenticated_auth(self):
+        """Test authenticated user linking"""
+        user = User.objects.create(username="foo", email="foo@bar.baz")
+        UserOAuthSourceConnection.objects.create(
+            user=user, source=self.source, identifier=self.identifier
+        )
+        request = get_request("/", user=user)
+        flow_manager = OAuthSourceFlowManager(
+            self.source, request, self.identifier, {"info": {}}, {}
+        )
+        action, connection = flow_manager.get_action()
+        self.assertEqual(action, Action.AUTH)
+        self.assertIsNotNone(connection.pk)
+        response = flow_manager.get_flow()
+        self.assertEqual(response.status_code, 302)
+
     def test_unauthenticated_link(self):
         """Test un-authenticated user linking"""
         flow_manager = OAuthSourceFlowManager(