We're using Shopify Buy buttons on a static site.
We offer digital goods to our users. They have accounts in our system that will receive the items they purchase on our storefront.
The user will authenticate on our store front to confirm their identity, and now I have their Account ID in that browser session.
When my backend server receives an `order/create` webhook, I need to know the purchaser's Account ID so I can automatically deliver their goods.
How can I get their Account ID from my shop's webpage to my backend webhook receiver?
Can I tie their Account ID to something like a Cart ID or Cart Token? Is that reliable?
Surely there's some way to know who placed the order on my backend server?