CodeIgniter is a PHP framework that will help you create web applications and web sites faster than writing code from scratch.
Login system
http://mfikri.com/en/blog/codeigniter-login
https://www.codexworld.com/codeigniter-user-registration-login-system/
https://www.webslesson.info/2018/10/user-registration-and-login-system-in-codeigniter-3.html
Forgot password function:
with token: https://www.youtube.com/watch?v=rzypoJWcsY0
http://findnerd.com/list/view/How-to-Make-Forgot-Password-in-Codeigniter/17641/
https://stackoverflow.com/questions/41216007/forgot-password-with-generated-code-in-codeigniter
https://www.studentstutorial.com/codeigniter/forgot-password