What is middleware in Laravel?

In Laravel, middleware is a layer of software that sits between the application and the HTTP request/response cycle. It can be thought of as a kind of “gatekeeper” that can perform various tasks on a request before it is passed on to the application or after it has been processed by the application and is being sent back to the user.

Middleware can be used to perform a variety of tasks, such as:

• Authenticating users
• Validating input data
• Modifying the request or response
• Caching responses
• Logging requests and responses
• Throttling requests
• etc.

In Laravel, middleware is defined as a class that implements the Handle method. This method receives the request and the closure (a callback function) that should be executed after the middleware. The middleware can then perform any logic it needs to before or after calling the closure.

Middleware is typically registered in the app/Http/Kernel.php file, where it can be assigned to specific routes or applied globally to all routes in the application.

For example, the following middleware class authenticates users and redirects them to the login page if they are not authenticated:

<?php

namespace App\Http\Middleware;

use Closure;
use Illuminate\Support\Facades\Auth;

class Authenticate
{
    public function handle($request, Closure $next)
    {
        if (Auth::guest()) {
            return redirect('login');
        }

        return $next($request);
    }
}

This middleware can then be assigned to a route like this:

Route::get('admin', ['middleware' => 'auth', function () {
    // Only authenticated users can access this route
}]);

Or it can be applied globally to all routes in the application by registering it in the $middleware property of the app/Http/Kernel.php file.