BigCommerce Custom App to integrate with my Real-time Shipping Quotes API

Hi guys!

Egor, a web developer from Moldova here

I'm looking for a way to integrate BigCommerce checkout with an external API (my own API)
This API will provide BigCommerce shoppers with Real-time Shipping Quotes based on their cart details and shipping address.

BigCommerce itself is already integrated with a limited list of Carriers,
but they don't allow any External API integrations
https://support.bigcommerce.com/s/article/Shipping-Methods?language=en_US#faq

So the goal is to build an app like this which integrates with my External API directly
https://www.bigcommerce.com/apps/optimal-ship-rates

There is one technical detail about this integration:
The shipping quotes my API returns have unique hashes as shipping method codes.
Meaning every time any shipping address field (or items) is updated,
shipping quotes received will be unique and the selected unique key should be saved as a shipping method of the order on order placement.

Let me know your thoughts on this!

Thanks!