These are actually things that our current customers have run into; our solution is reasonably generic. I've touched at your points below.

re: databases, one option is pointing your Reploy environment to a common database. The other is to actually spin up a database within Reploy, where you seed data or a do a dump (pgdump, mongodump, etc..)

re: logins, we generate deterministic URLs (checkout https://docs.getreploy.com/docs/links-discovery), so you can tell your auth provider what the links will look like. (Can talk more about this if you like).