Reverse-proxy authentication for App Platform app

Looking for advice on best practice and feasibility. I want to put a pre-existing custom app (Shiny/R-based) behind a reverse proxy for authentication (password-protection) purposes, using oauth2_proxy, nginx or ShinyProxy.

I don’t want to spend lots of time on infrastructure as this is not my main job – I’d like the convenience of the App Platform to update and manage the app itself, but how best to integrate a reverse proxy? Most of the online tutorials I’ve found (some examples below) suggest using docker-compose.yml to launch the multiple services (which is not applicable to DO App Platform as far as I can tell).

Is it better to integrate installation of the proxy into the app’s DOCKERFILE, or is there some more sensible way to run a reverse proxy to protect the app behind authentication? Droplet? Or do I need to look into Kubernetes instead of App Platform?

• https://github.com/ARCLeeds/oauth2-proxy-shiny/tree/main/shiny-example
• https://www.digitalocean.com/community/tutorials/how-to-use-traefik-v2-as-a-reverse-proxy-for-docker-containers-on-ubuntu-20-04
• https://developer.okta.com/blog/2022/07/14/add-auth-to-any-app-with-oauth2-proxy