How can I use middleware for authentication? about wp-slim-framework

[Botnary]

If you use Slim Framework as a Wordpress plugin then in your routes you have access to Wordpress API.
i would do something like this:

add_action('slim_mapping',function($app){
    $app->get('/slim/api/books',function(){
        //wordpress current user
        $user = wp_get_current_user(); // this function returns current user as a Wp_User object.
        if($user->ID > 0) { // it means that there is a user online
            //do something as logged in user.
        }
    });
});

and actually this is how i do it, and i don't use any middlewares.
Also you should not access directly Slim files with include, but use composer autoloader.
So in your code if you need any class from Slim just do this:

use \Slim\Middleware;
$auth = new HttpBasicAuth();

and autoloader will find the required file automatically for you.