I've finally managed to get what I need working with the adLDAP and SSO.
For future reference for anyone else looking for similar solution to get the firstname and lastname from Active Directory that matches the logged on users username...
<?php
session_start();
$username = explode('\\',$_SERVER["LOGON_USER"]);
$_SESSION['username'] = strtolower($username[1]);
?>
<?php
include ("/../src/adLDAP.php");
$ldap=new adLDAP();
$userinfo = $ldap->user()->info($_SESSION['username'],array("givenname","sn"));
$_SESSION['firstname'] = $userinfo[0][givenname][0];
$_SESSION['lastname'] = $userinfo[0][sn][0];
$firstname = $_SESSION['firstname'];
$lastname = $_SESSION['lastname'];
?>
<br />
<strong>Welcome </strong><?php printf("<b><i>$firstname $lastname</i></b>"); ?>