Which user bought something

Hello,

When a customer creates an account on wordpress, and they use your plugin to buy something from stripe, how does the code know which user bought the product? How can i get the wordpress user_ID so i can tie the product to a particular user? What good is it if i cant know which user bought an item so i can enable that website feature for that particular logged in user, especially when they are paying each month, i have to know to reenable that feature for that user.

Thanks