headers.php

<?php

$app->after(function(Request $request, Response $response) {
    $cors = array(
        'Access-Control-Allow-Origin'  => '*',
        'Access-Control-Allow-Methods' => 'POST',
        'Access-Control-Allow-Headers' => 'content-type, x-requested-with'
    );

    foreach ($cors as $name => $value) {
        $response->headers->set($name, $value);
    }
});

OPTIONS.php

<?php

$app->match('/link', function() use ($app) {
    return new Response('', 200);
})->method('OPTIONS');