Get Session Info Outside Codeigniter

I have a problem about reading session data outsite codeigniter.
I'm using ResponsiveFileManager project for file/folder operations. 
If the user copy responsivefilemanager path in page source, unauthenticated user can use this library. 
I'm try to check userdata from responsivefilemanager config file but \Config\Services can't be reached. 

Code:

require __DIR__ . '/../../vendor/autoload.php';

$loginCheck = \Config\Services::BackendAuthService()->isLoggedIn();
if (! $loginCheck) {
    header("HTTP/1.1 401 Unauthorized");
    exit;
}

Folder structure,
- app
- public
- filemanager
-system
-Thirdparty 
...
How can i use codeigniter autoload in another library.
Thanks.