It depends on what exactly your app is because you might be able to use existing solutions.

But my recommendation is Firebase or Supabase. These tools were basically designed for this type of webapp. I know a team of junior devs who created a production-app in a few weeks with Firebase. Firebase handles authentication, the database REST endpoint, and various other common webapp functionality, so that stuff is seriously achievable in hours. In Supabase "signup", "login", "login with provider", "send reset email" are all single JS functions.