Login page before showing my Retool app

I've seen the Retool docs for the REST-API login. But it's less/less explained for a simple problem?
My goal is to show a username and password form BEFORE my Retool app opens up. The username and password can be fetched from my Remote database (postgres) URI.

So yea, a user must be a part of my auth-table to view my Retool app.
If anyone can point to a simple solution, it'll be very much helpful.
Thanks for your time!