Fix method visibility.

src/Controller/Component/AuthComponent.php

@@ -280,7 +280,7 @@ class AuthComponent extends Component
      * @param \Cake\Event\Event $event Event instance.
      * @return void|\Cake\Network\Response
      */
-    public function _authCheck(Event $event)
+    protected function _authCheck(Event $event)
     {
         $controller = $event->subject();
 

tests/test_app/TestApp/Controller/Component/TestAuthComponent.php

@@ -22,7 +22,7 @@ use Cake\Event\Event;
  */
 class TestAuthComponent extends AuthComponent
 {
-    public function _authCheck(Event $event)
+    protected function _authCheck(Event $event)
     {
         if (isset($this->earlyAuthTest)) {
             $this->authCheckCalledFrom = $event->name;