For adjunct pieces such as web app authentication, including some common features such as user sign up via email or phone, recover a password, multi-factor auth, social sign in, and the like, there's not yet a good solution (AFAIK).
I will gladly donate money toward developers working on this, especially if it's something simple such as Elixir Phoenix `mix phx.gen.auth` doing a one-time setup with good defaults, then fully customizable.