PHP框架中的安全措施是如何实现的？

use Illuminate\Http\Request;
use Illuminate\Validation\Rule;

class FormController extends Controller
{
    public function submit(Request $request)
    {
        $request->validate([
            'name' => 'required|max:255',
            'email' => 'required|email',
            'age' => 'required|integer|between:1,150',
        ]);
    }
}

use Illuminate\Database\Eloquent\Builder;

class UserController extends Controller
{
    public function find()
    {
        $name = 'John Doe';
        $users = User::where('name', '=', $name)->get();
    }
}

use Illuminate\Support\Facades\Html;

class HtmlController extends Controller
{
    public function renderHtml()
    {
        $html = '<b>Hello, ' . Html::encode($name) . '!</b>';
    }
}

use Illuminate\Support\Facades\Session;

class FormController extends Controller
{
    public function display()
    {
        return view('form', [
            'csrf_token' => Session::token(),
        ]);
    }
}

use Helmet;

class BaseController extends Controller
{
    public function __construct()
    {
        $this->middleware(Helmet::class);
    }
}

$username = $request->get('username');
$user = User::where('username', '=', $username)->first();