Fix security vulnerability in admin modules

- The Module\BaseAdmin::post method checked credentials but didn't abort the process when it failed
- Created Module\BaseAdmin::checkAdminAccess method

src/Module/Admin/PhpInfo.php

@@ -27,7 +27,7 @@ class PhpInfo extends BaseAdmin
 {
 	public static function rawContent(array $parameters = [])
 	{
-		parent::rawContent($parameters);
+		self::checkAdminAccess();
 
 		phpinfo();
 		exit();