The plugin works, but maybe you would first learn java and the method naming convention itself, packages and clean code rules (Like not making If's pyramid for example). Btw, if the Api-version is 1.16, the plugin will still work, and on other versions too, so maybe you would do that ? Anyway, I wouldn't use it myself, it's primitive and ugly written. A better replacement is even the famous AuthMe, which has many more options and is better written.

If you want to knock out a login plugin more, then shine with something that has some better stuff than just /register/login/changepassword, because that's what every plugin has -_-, you could even make an automatic login for people with a premium account (People who really bought minecraft).