<?php

class Student extends User implements StudentInterface
{

    public function setPassword($psswd)
    {
        if(is_string($psswd)) {
            $this->password = $psswd;
        }else {
            throw new Exception("Error Processing Request", 1);
        }
    }

    public function auth($account, $psswd, AuthServices $auth) : boolean
    {
	if($psswd == ""){
	    return false;
        }
        return true;
    }

}

class AuthServices {

    public function auth(User $user)
    {
        if($user->getPassword() === $dbPassword){
            //do something...
        }
    }

}

/**
 * Whatever...
 */

interface StudentInterface
{
    public function setPassword($psswd);
}


abstract class User {

    public $id;
    protected $password;

    abstract protected function auth($account, $psswd, AuthServices $auth) : boolean;

}



$user = new Student();
$user->setPassword("hfudslafh");

print_r($user);