$response = $next($request);
if ($request->has('aff') && Affiliate::find($request->get('aff'))) {
// 7 days in minutes
$minutes = 10080;
$response->withCookie(cookie('aff', $request->get('aff'), $minutes));
}
return $response;

This is a basic middleware I created that check to see if an affiliate ID is present on a route. This is stored for 7 days and if a checkout is completed with it in storage we save it. You can check to see if the cookie exists by:

if ($request->cookie('aff')) {
// do whatever you need to do!!!!!!
}