We have a SaaS system called Catermonkey, and we want to integrate with Shopify.
Basically we want this:
Customer orders food in a shopify store
The order is synced to catermonkey (we provide tools for Chefs to prepare the meals, like recipes, ingredients etc.)
The order is synced through a webhook
But Catermonkey is a stand-alone tool with no freemium. In the case somebody coming from Shopify, clicking 'install app', I'd like to show a 'log in screen', asking the user to sign up / sign in with us.