PHP- No option to authenticate user in firebase-php

I am trying to identify if I have set security rules in the users node like below

Users:
  $uid:
    write: auth.uid != null,
    read : auth.uid != null,

What I don't understand how to authenticate users with PHP. As document doesn't provide me any sign-in functionality as in JavaScript .Because until and unless I authenticate the user. It doesn't allow me to update values in user's nodes due to security rules.

Using laravel/firebase-php V4.29
Firebase SDK 8.4
Language - PHP

via Chebli Mohamed