What are middleware in Laravel?

In Laravel, middleware are a type of filtering mechanism that sits between a request and the application's response. Middleware is primarily used to inspect and modify incoming HTTP requests before they reach the controller, and it can also manipulate the response before it is sent back to the client.

Here are some common uses of middleware in Laravel:

1. Authentication: Ensuring that a user is authenticated before they can access specific routes.
2. Logging: Logging the details of every request that comes into your application.
3. CSRF Protection: Verifying that the request's CSRF token is valid.
4. CORS (Cross-Origin Resource Sharing): Controlling which domains are allowed to access your resources.
5. Rate Limiting: Restricting the number of requests a client can make to your API.

Example:

Creating a middleware:

php artisan make:middleware CheckAge

This will generate a file in app/Http/Middleware/CheckAge.php, where you can define logic for filtering requests:

public function handle($request, Closure $next)
{
    if ($request->age <= 18) {
        return redirect('home');
    }

    return $next($request);
}

Here, if the age in the request is less than or equal to 18, the user is redirected to the home page; otherwise, the request is allowed to proceed.

Registering Middleware:

Middleware can be registered globally (applies to all routes) or assigned to specific routes in the app/Http/Kernel.php file.