How can I safely implement my login routes?

I am currently making a login and registration system as a project for a website, but I am uncertain of how I can safely implement the routes/logic for it. Currently, in my client side code I send a fetch request to my login or register route, and do the logic there, and then send a JSON object back, which is manipulated whether there is an error or not, and I have implemented CORS and Header (Origin and Referrer headers) authorization middleware within my POST routes, so no external script can mass produce users/login [aka brute force]. Is there another safer and better way of handling this?