tobajetex/mern-advanced-auth ? reverse-engineered prompt

Build me a MERN style authentication app, or at least the backend for it, with user signup, login, logout, and protected routes. I want someone to be able to create an account, sign in, stay logged in, and only access private data when they are authenticated.

Please keep it simple to run locally, with clear setup steps and any needed environment variables explained in plain English. Add sensible security basics, clean error messages, and a straightforward way to test the auth flow from the API. If it makes sense, leave the code ready for things like password reset, email verification, and future user profile features later on.

Make the result clean and easy to understand, and if you need current docs for anything, look them up online first.