Get windows username under IIS

Im trying to create a simple page, and at the top say

Welcome User

I would like to get the windows username and replace user in Welcome, so for example 'Welcome tcross'.

Reading some documents this should be easy as Im using PHP under IIS, so I should be able to use:-

<?php
	echo $_SERVER['LOGON_USER'];
	echo $_SERVER['AUTH_USER'];
	echo $_SERVER['REDIRECT_LOGON_USER'];
	echo $_SERVER['REDIRECT_AUTH_USER'];
?>

Select allOpen in new window

But all I get is:-

Notice: Undefined index: REDIRECT_LOGON_USER in C:\inetpub\wwwroot\test.php on line 4

Notice: Undefined index: REDIRECT_AUTH_USER in C:\inetpub\wwwroot\test.php on line 5

Is there something Im missing? Is there something I need to enable in IIS?

Thank you