LoginSecurity is a simple, light, fast and secure user authentication management system first created in 2012. It's core focus is to be simple to setup up and use.
Version hosted in TeTeOS.Net: [You can download with wget]
Plugin version: 3.1
Tested MC versions: 1.8 - 1.17
If your server version is 1.17 or highter, you can try newer alternative:
NexAuth : https://www.teteos.net/d/267-minecraft-plugin-nexauth-java