Learnings about authentication and authorization.

At the beginning of my Engineering career, I worked in a place where I had a lot of freedom to implement and experiment any technology I found interesting. I tried many technologies like PHP, Java, EJBs, SOAP, Rest and JavaScript. This gave me a lot of perspective, but I lacked the guidance and mentoring from more experienced developers. One of the most problematic things I built was a login. I would like to share in this document things that I did in the past so you understand why it is problematic and how I would build them today. Earlier Mistakes My First PHP Login. This is not a terrible option when using a single host, small project, but the biggest problem comes when we need to scale horizontally. Session variables exist only on the servers they are created. If you add more servers + Load Balancer, there is no guarantee that your requests go to the same server. In terms of vulnerabilities, if somebody manages to read your session id, they can impersonate you, act on your behalf. This is not really different from other methods like JWT so it is important to set up SameSite cookies or CSRF tokens, but do you think I did that for my first login ? of course NOT! My first Password storage. If you are thinking on implementing a login please NEVER do what I am about to describe: The first time I implemented a password, I was worried that somebody would find out the "actual" password. I wasn't actually thinking about using HTTP (instead of HTTPs), so my take on this was "encrypting" the password into MD5. Then the password was saved in MD5, but I was NOT doing anything different than just sending the password AS is. Let me explain the problems with this approach: Over HTTP an MD5 password can be read, and anybody can simply replicate the request with the same MD5 MD5 was actually NOT encrypting, it was a hashing. There are databases all over the internet mapping MD5 and other hashed passwords available so finding an MD5 can actually be translated to an actual password