Login on centos, using unix user and password on php

Login.php

<?php 
class Login{

static function authenticate($user, $pass){
  $shad =  preg_split("/[$:]/",`cat /etc/shadow | grep "^$user\:"`);
  $mkps = preg_split("/[$:]/",trim(`mkpasswd -m sha-512 $pass $shad[3]`));
  return ($shad[4] == $mkps[3]);
}
public function handleAuth($user,$pass){
	return $this->authenticate($user,$pass);
}
}
$login = new Login();
(bool) $login::handleAuth('user','pass'); 
?>