Middleware in Laravel: A Comprehensive Guide
https://algocodersmind.com/middleware-in-laravel-a-comprehensive-guide/

Laravel 5 Middleware tutorial
Laravel 5 – Middleware Tutorial : https://tutorialedge.net/laravel-5-middleware-routing-tutorial

This tutorial serves as a more expanded introduction to Laravel 5.1’s middleware than that of the documentation.

Manual – HTTP Middleware : https://laravel.com/docs/5.2/middleware#introduction