auth_middleware.php

<?php

$app = new Silex\Application();

$app = (new Stack\Builder())
    ->push('Dflydev\Stack\BasicAuthentication', [
        'firewall' => [
            ['path' => '/', 'anonymous' => true],
            ['path' => '/login'],
        ],
        'authenticator' => function ($username, $password) {
           // authenticate
        },
        'realm' => 'here there be dragons',
    ])
    ->resolve($app);

$request = Request::createFromGlobals();
$response = $app->handle($request)->send();