From 884042952f8d610030723a3b6e165090b6bf5356 Mon Sep 17 00:00:00 2001
From: Ayumi Hamasaki <asianspawebsite@gmail.com>
Date: Tue, 25 Jun 2019 15:15:11 +0100
Subject: [PATCH] Block off SW running in backend and reduce lookups (#4385)

Credit to @ayumihamsaki. Related #4384
---
 config/cms.php                                | 22 +++++++++++++++++++
 .../backend/assets/js/auth/uninstall-sw.js    | 10 ---------
 modules/backend/controllers/Auth.php          |  2 --
 modules/backend/layouts/_head.htm             | 18 +++++++++++++++
 modules/backend/layouts/auth.htm              | 18 +++++++++++++++
 5 files changed, 58 insertions(+), 12 deletions(-)
 delete mode 100644 modules/backend/assets/js/auth/uninstall-sw.js

diff --git a/config/cms.php b/config/cms.php
index 75189b297..a2b2fb5af 100644
--- a/config/cms.php
+++ b/config/cms.php
@@ -413,4 +413,26 @@ return [
 
     'restrictBaseDir' => true,
 
+    /*
+    |--------------------------------------------------------------------------
+    | Backend Service Worker
+    |--------------------------------------------------------------------------
+    |
+    | Allow plugins to run Service Workers in the backend.
+    |
+    | WARNING: This should always be disabled for security reasons as Service
+    | Workers can be hijacked and used to run XSS into the backend. Turning
+    | this feature on can create a conflict if you have a frontend Service
+    | Worker running. The 'scope' needs to be correctly set and not have a
+    | duplicate subfolder structure on the frontend, otherwise it will run
+    | on both the frontend and backend of your website.	
+    |
+    | true  - allow service workers to run in the backend
+    |
+    | false - disallow service workers to run in the backend
+    |
+    */
+
+    'enableBackendServiceWorkers' => false,	
+
 ];
diff --git a/modules/backend/assets/js/auth/uninstall-sw.js b/modules/backend/assets/js/auth/uninstall-sw.js
deleted file mode 100644
index eb48b3938..000000000
--- a/modules/backend/assets/js/auth/uninstall-sw.js
+++ /dev/null
@@ -1,10 +0,0 @@
-// Only run on HTTPS connections
-if (location.protocol === 'https:') {
-    // Unregister all service workers before signing in to prevent cache issues
-    navigator.serviceWorker.getRegistrations().then(
-        function(registrations) {
-            for (let registration of registrations) {  
-                registration.unregister();
-            }
-    });
-}
\ No newline at end of file
diff --git a/modules/backend/controllers/Auth.php b/modules/backend/controllers/Auth.php
index 42f80bcf7..efb120ba9 100644
--- a/modules/backend/controllers/Auth.php
+++ b/modules/backend/controllers/Auth.php
@@ -46,8 +46,6 @@ class Auth extends Controller
             })->only('signout');
         }
 
-        // Add JS File to un-install SW to avoid Cookie Cache Issues when Signin, see github issue: #3707
-        $this->addJs(url("/modules/backend/assets/js/auth/uninstall-sw.js"));
         $this->layout = 'auth';
     }
 
diff --git a/modules/backend/layouts/_head.htm b/modules/backend/layouts/_head.htm
index 0edbc4803..68033f741 100644
--- a/modules/backend/layouts/_head.htm
+++ b/modules/backend/layouts/_head.htm
@@ -39,6 +39,24 @@
     <link href="<?= $script . '?v=' . $coreBuild; ?>" rel="preload" as="script" importance="high">
 <?php endforeach; ?>
 
+<?php if (!Config::get('cms.enableBackendServiceWorkers', false)) : ?>
+    <script>
+        "use strict";
+        /* Only run on HTTPS connections
+         * Block off Front-end Service Worker from running in the Backend allowing security injections, see GitHub #4384
+         */
+         if (location.protocol === 'https:') {
+             // Unregister all service workers before signing in to prevent cache issues, see github issue: #3707
+             navigator.serviceWorker.getRegistrations().then(
+                 function(registrations) {
+                     for (let registration of registrations) {  
+                         registration.unregister();
+                     }
+                 });
+         }		
+    </script>
+<?php endif; ?>
+
 <?= $this->makeAssets() ?>
 <?= Block::placeholder('head') ?>
 <?= $this->makeLayoutPartial('custom_styles') ?>
diff --git a/modules/backend/layouts/auth.htm b/modules/backend/layouts/auth.htm
index 6f7bc0ec4..e28b2e555 100644
--- a/modules/backend/layouts/auth.htm
+++ b/modules/backend/layouts/auth.htm
@@ -37,6 +37,24 @@
             <link href="<?= $script . '?v=' . $coreBuild; ?>" rel="preload" as="script" importance="high">
         <?php endforeach; ?>
 
+        <?php if (!Config::get('cms.enableBackendServiceWorkers', false)) : ?>
+            <script>
+                "use strict";
+                /* Only run on HTTPS connections
+                 * Block off Front-end Service Worker from running in the Backend allowing security injections, see GitHub #4384
+                 */
+                 if (location.protocol === 'https:') {
+                 // Unregister all service workers before signing in to prevent cache issues, see github issue: #3707
+                 navigator.serviceWorker.getRegistrations().then(
+                     function(registrations) {
+                         for (let registration of registrations) {  
+                             registration.unregister();
+                         }
+                     });
+                 }		
+            </script>
+        <?php endif; ?>
+
         <?= $this->makeAssets() ?>
         <?= Block::placeholder('head') ?>
         <?= $this->makeLayoutPartial('custom_styles') ?>