Simple custom user field

[T3db0t]

I'm building a SaaS, and I'll be using Stripe for monthly recurring payment. What's the best way to indicate that a user is "premium" and should have the appropriate permissions? I'd expect to use a Stitch Function to receive the approval callback, but what then?

I'd love to avoid having to maintain my own users collection (which would have to be synced with triggers...). Any ideas?

—Ted