Creating customers in Stripe from Shopify

[DropTilYouShop]

Our Shopify site uses Stripe as payment provider. When a transaction is processed, Stripe automatically creates a customer in guest mode. We want a normal/non-guest customer to be created in Stripe, and associate the payment method with that customer (you cannot do that with a guest customer). The goal is to be able to charge the customer automatically for a subscription a year after the purchase. How do we do that? In other sales channels, which we coded ourselves, is was not difficult. But I do not see a way to do this in Shopify.