Hi Colin!

On your backend, Clerk gives you a stable User ID for each user. You're free to use it as a foreign key in your database as you normally would. (clerk.dev runs on clerk, and that's how we do it internally)

We only have a Node SDK so far - here's a guide on retrieving the User ID from your backend: https://backend-docs.clerk.dev/quick-starts/next.js-api-rout...

Soon we will launch a way to add custom attributes to the user object, as well as management of those attributes in the UI if desired. Things can get a bit murkier there, but those features will always only be opt-in.