How can I find the checkout token using the Checkout API?

[sebastiandev]

Hello,

We are creating an app that will use the Carrier Service API. I would like to obtain more information regarding the cart/checkout, but I do not have any checkout token. Is it possible to find the checkout token by using the Checkout API during a Carrier Service request from Shopify?

Additionally, I have some extra information in the cart attributes which is important for calculation.