Add subscription details to user for better-auth

[nperez0111]

It'd be a really nice integration with Better-Auth, if we added a column for each user to store their current subscription status.

To give more context, in my website, I wanted to check the subscription status of the current signed in user, but not have to hit the Polar API for each request (why hit the Polar API when I already have access to my own DB).

So, what I did was add an additionalField to each of my users, and use the webhook events to change the subscription status of the user whenever the subscription changed:

https://github.com/TypeCellOS/BlockNote/blob/7fcafe493a7aa4d67eae147b03023165dd8d18a5/docs/auth.ts#L222-L248

This seems like it will work pretty well and reduce dependence on hitting the polar API for each one of my requests.

So, for the better-auth polar adapter, I think it would be great to add a new column for users which is a JSON.stringify'd version of the current subscription details. Then it would make it easy to access the current subscription state, rather than hitting the Polar API for it.

[pieterbeulque]

That's good feedback, but I'm not 100% sure if we should do something opinionated here or if we'd leave that to the implementation.

I don't think there's a turn-key solution to this. Storing the full customer state could be a middle ground, but that would still require a webhook setup to keep things in sync. That'd require a developer to go into Polar to set up that webhook, and things wouldn't be as batteries-included as they appear.