Also there already exists this reverse engineered project: https://github.com/ByteSizedMarius/rewerse-engineering/
I do have a suggestion for your app though: Have it compare your basket of goods across different markets in your region to show you the cheapest option. I'm pretty sure this possibility is actually one of the reasons they locked down the API.
I've used Data from REWE in the past and made a comparison between a couple of cities in Germany (I believe it was Frankfurt, cologne, Berlin, Munich and Hamburg). Hamburg was by far the most expensive, often as much as 10-20% more expensive.
I'd settle for just being able to sort items by unit price... I'm sure this is a [regulation-]solved problem in Germany though
It can search for items, add them to the basket, picks a delivery slot and does the checkout.
With a little more scaffolding in markdown files, this now takes care of my weekly shopping.
Haskell is indeed an interesting choice. ;)
Did you implement your own OAUTH2 flow in haskell for this?
Until it breaks in a few weeks.