使用Windows身份验证作为Intranet应用程序的登录凭据

I'm working on an intranet web application in PHP. Im trying to use Windows NT login credentials to logon to the application. The trouble im having here is how do i get the remote users windows username? I want to obtain the username and then check against various LDAP groups so that I can direct them to appropriate pages in my application.I'm working on an intranet web application in P