Querying user data from another site to attach a subscription

[tarnold]

I have a website (e.g. example.com) and have attached my Shopify store to shop.example.com. I'd like to be able to query the user's information from example.com that can then be used in their shop.example.com experience. (e.g. pre-populate a list with information they've already entered on their account on example.com).

Would I need to create our own app, webhooks or API calls to have this kind of integration?