$_SERVER['PHP_AUTH_PW'] is not populating after NTLM authentication in php script

Question

I am trying to have $_SERVER['PHP_AUTH_PW'] in my php script. I am using NTLM authentication in Apache 2.4.9.

In my vhost.conf I have

   <Directory "C:\xampp\htdocs\project">
       AuthName "NTLM Login" 
       AuthType SSPI
       SSPIAuth on
       SSPIAuthoritative off 
       SSPIOmitDomain on 
       SSPIOfferBasic on 
       require valid-user 
    </Directory>

In my php script $_SERVER['PHP_AUTH_USER'] is set, but $_SERVER['PHP_AUTH_PW'] is not set. I need to call another service using those username and password. Can anyone please help me?