How to get cart details & and its token to access buybutton for given customer id

[KumaraSwamyY]

Here is the use case:

1. All the products showing in internal application. And from cart rest of the work flow (cart, checkout, payment..etc) with shopify.
2. Buy button iframe integrated with shopify productid and token , its fine for guest flow.  We want to handle this for existing customers. 
   
   1. How to get cart id & token for existing customer to enable shopify session for cart and its checkout flow.
   2. If it's a new customer, how to create new cart and map with customer.

I am happy to connect with you over the call, so that we can discuss.

[Zqdo]

Is this something that you're looking to set up?