Add the framesrc csp by default

lib/AppInfo/Application.php

@@ -27,12 +27,14 @@
 
 namespace OCA\Files_PDFViewer\AppInfo;
 
+use OCA\Files_PDFViewer\Listeners\CSPListener;
 use OCA\Files_PDFViewer\Listeners\LoadViewerListener;
 use OCA\Viewer\Event\LoadViewer;
 use OCP\AppFramework\App;
 use OCP\AppFramework\Bootstrap\IBootContext;
 use OCP\AppFramework\Bootstrap\IBootstrap;
 use OCP\AppFramework\Bootstrap\IRegistrationContext;
+use OCP\Security\CSP\AddContentSecurityPolicyEvent;
 use OCP\Util;
 
 class Application extends App implements IBootstrap {
@@ -44,6 +46,7 @@ public function __construct() {
 
 	public function register(IRegistrationContext $context): void {
 		$context->registerEventListener(LoadViewer::class, LoadViewerListener::class);
+		$context->registerEventListener(AddContentSecurityPolicyEvent::class, CSPListener::class);
 	}
 
 	public function boot(IBootContext $context): void {

lib/Listeners/CSPListener.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * @copyright Copyright (c) 2020, Roeland Jago Douma <roeland@famdouma.nl>
+ *
+ * @author Roeland Jago Douma <roeland@famdouma.nl>
+ *
+ * @license GNU AGPL version 3 or any later version
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+namespace OCA\Files_PDFViewer\Listeners;
+
+use OCP\AppFramework\Http\EmptyContentSecurityPolicy;
+use OCP\EventDispatcher\Event;
+use OCP\EventDispatcher\IEventListener;
+use OCP\Security\CSP\AddContentSecurityPolicyEvent;
+
+class CSPListener implements IEventListener {
+	public function handle(Event $event): void {
+		if (!$event instanceof AddContentSecurityPolicyEvent) {
+			return;
+		}
+
+		$csp = new EmptyContentSecurityPolicy();
+		$csp->addAllowedFrameDomain('\'self\'');
+		$event->addPolicy($csp);
+	}
+}