Avoid a notice in HTTP signature check, preparation for authentication

src/Module/Outbox.php

@@ -8,6 +8,7 @@ use Friendica\BaseModule;
 use Friendica\Protocol\ActivityPub;
 use Friendica\Core\System;
 use Friendica\Model\User;
+use Friendica\Util\HTTPSignature;
 
 /**
  * ActivityPub Outbox
@@ -29,6 +30,9 @@ class Outbox extends BaseModule
 
 		$page = defaults($_REQUEST, 'page', null);
 
+		/// @todo Add Authentication to enable fetching of non public content
+		// $requester = HTTPSignature::getSigner('', $_SERVER);
+
 		$outbox = ActivityPub\Transmitter::getOutbox($owner, $page);
 
 		header('Content-Type: application/activity+json');