AC-12731 Issue#39020 Rendering the critical css inline event via csp inline secure render

Author: Mohamed-Asar

app/code/Magento/Theme/Controller/Result/AsyncCssPlugin.php

@@ -7,6 +7,7 @@
 
 namespace Magento\Theme\Controller\Result;
 
+use Magento\Csp\Api\InlineUtilInterface;
 use Magento\Framework\App\Config\ScopeConfigInterface;
 use Magento\Store\Model\ScopeInterface;
 use Magento\Framework\App\Response\Http;
@@ -26,12 +27,21 @@ class AsyncCssPlugin
      */
     private $scopeConfig;
 
+    /**
+     * @var InlineUtilInterface
+     */
+    private $cspInlineUtil;
+
     /**
      * @param ScopeConfigInterface $scopeConfig
+     * @param InlineUtilInterface $cspInlineUtil
      */
-    public function __construct(ScopeConfigInterface $scopeConfig)
-    {
+    public function __construct(
+        ScopeConfigInterface $scopeConfig,
+        InlineUtilInterface $cspInlineUtil
+    ) {
         $this->scopeConfig = $scopeConfig;
+        $this->cspInlineUtil = $cspInlineUtil;
     }
 
     /**
@@ -99,10 +109,13 @@ private function extractLinkTags(string &$content): string
                 $media = $mediaAttribute[2];
             }
             $media = $media ?? 'all';
-
+            $onload = $this->cspInlineUtil->renderEventListener(
+                'onload',
+                sprintf('this.onload=null;this.media=\'%s\'', $media)
+            );
             $style = sprintf(
-                '<link rel="stylesheet" media="print" onload="this.onload=null;this.media=\'%s\'" href="%s">',
-                $media,
+                '<link rel="stylesheet" media="print" %s href="%s">',
+                $onload,
                 $href
             );
             $styles .= "\n" . $style;