SessionProvider or equivalent for SvelteKit

[pauldemarco]

Goals

1. Session should be reactive on the client
2. A signOut on one tab should show user as signed out on the other tab
3. Some Pure-js modules require listening to auth state changes, so something like onSessionChanged would be nice.

Non-Goals

Background

Auth.js should provide a reactive session, much like the SessionProvider in next-auth/react:
https://github.com/nextauthjs/next-auth/blob/main/packages/next-auth/src/react/index.tsx#L340

Proposal

In a similar fashion, utilizing local storage within the SessionProvider to keep different tabs in sync.
I'm sure how to integrate with a SvelteKit project, perhaps useContext? Or just some global function onSessionChanged we can subscribe to?