Restrict who can use the lastSeenAt user sort

src/Api/Controller/ListUsersController.php

@@ -76,6 +76,13 @@ protected function data(ServerRequestInterface $request, Document $document)
 
         $actor->assertCan('viewUserList');
 
+        if (! $actor->hasPermission('user.viewLastSeenAt')) {
+            // If a user cannot see everyone's last online date, we prevent them from sorting by it
+            // Otherwise this sort field would defeat the privacy setting discloseOnline
+            // We use remove instead of add so that extensions can still completely disable the sort using the extender
+            $this->removeSortField('lastSeenAt');
+        }
+
         $filters = $this->extractFilter($request);
         $sort = $this->extractSort($request);
 

tests/integration/api/users/ListTest.php

@@ -91,6 +91,49 @@ public function shows_full_results_without_search_or_filter()
         $this->assertEquals(['1', '2'], Arr::pluck($data, 'id'));
     }
 
+    /**
+     * @test
+     */
+    public function allows_last_seen_sorting_with_permission()
+    {
+        $this->prepareDatabase([
+            'group_permission' => [
+                ['permission' => 'viewUserList', 'group_id' => 2],
+                ['permission' => 'user.viewLastSeenAt', 'group_id' => 2],
+            ],
+        ]);
+
+        $response = $this->send(
+            $this->request('GET', '/api/users')
+            ->withQueryParams([
+                'sort' => 'lastSeenAt',
+            ])
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+    }
+
+    /**
+     * @test
+     */
+    public function disallows_last_seen_sorting_without_permission()
+    {
+        $this->prepareDatabase([
+            'group_permission' => [
+                ['permission' => 'viewUserList', 'group_id' => 2],
+            ],
+        ]);
+
+        $response = $this->send(
+            $this->request('GET', '/api/users')
+                ->withQueryParams([
+                    'sort' => 'lastSeenAt',
+                ])
+        );
+
+        $this->assertEquals(400, $response->getStatusCode());
+    }
+
     /**
      * @test
      */