swatimj29/mern-login-backend ? reverse-engineered prompt

Build me the backend for a simple MERN app that handles user signup, login, and logout. I want users to be able to create an account with email and password, sign in securely, and get back a token they can use to stay logged in and access protected routes. Please store users in a database, hash passwords properly, and add basic validation and error messages for bad input or wrong credentials.

I also want a small protected test route so I can confirm the login is working, plus a clean setup for environment variables, database connection, and CORS so it can connect to a frontend later. Keep it simple and easy to run locally, and make sure the code is organized clearly enough that I can extend it later for things like profile pages or password reset. If you need to check current best practices or docs online, go ahead and do that.