routes.php

<?php

Route::post('test', 'TestController@store');

TestController.php

<?php

namespace App\Http\Controllers;

use App\Http\Requests\TestRequest;

class TestController extends Controller
{
    public function __construct()
    {
        $this->middleware('test');
    }
    
    public function store(TestRequest $request)
    {
        dd($request->all());
    }
}

TestMiddleware.php

<?php

namespace App\Http\Middleware;

use Closure;

class TestMiddleware
{
    /**
     * Handle an incoming request.
     *
     * @param  \Illuminate\Http\Request  $request
     * @param  \Closure  $next
     * @return mixed
     */
    public function handle($request, Closure $next)
    {
        $request->replace(['test' => 'testing']);

        return $next($request);
    }
}

TestRequest.php

<?php

namespace App\Http\Requests;

use App\Http\Requests\Request;

class TestRequest extends Request
{
    /**
     * Determine if the user is authorized to make this request.
     *
     * @return bool
     */
    public function authorize()
    {
        return true;
    }

/*
    public function validate()
    {
        dd($this->all());
    }
*/

    /**
     * Get the validation rules that apply to the request.
     *
     * @return array
     */
    public function rules()
    {
        return [
            'name' => 'required',
            'content' => 'required'
        ];
    }
}