Hi,
1. Are you sure ? That's not what I see on my end. On my end, the link I get on the frontend as customer is always a HikaShop link (which checks on the download restrictions you can configure in the backend). And when I click on the link, HikaShop does these checks and then redirects to the link you put there.
The link would only be in clear if you were using a custom product field to add it to the products instead of using the "Images and Files" area of the product edition page.
2. In that case, you want to use HikaSubscriptions:
www.hikashop.com/component/hikashop/prod...ikasubscription.html
With it, you can add the user to a subscription after the purchase and make it so that the subscription expires after 30 days. Then, you can configure the subscription to give access to a user group, etc.