Recurring application charge callback with App Bridge

I’m building a Shopify app which does not use any cookies and uses the App Bridge session.

I’ve created a recurring application charge which has the return url set to [https://myapp.com/recurring-application-charge/callback](https://myapp.com/recurring-application-charge/callback) and Shopify attaches the charge ID once the user accepts the charge.

https://myapp.com/recurring-application-charge/callback?charge_id=12345678

The charge_id alone is not enough for me to do anything with as I need to know the store ID to be able to make any actions.

How should I get the store if all I am provided is the charge_id?

It turns out I can just append ?shop={shop} to the end of my return url and that lets me know the store from the callback.