c# - ASP.NET Windows Authentication Login screen -

i have ipad app , looking add authentication it. have login page username , password field in app.

now able send username , password asp.net api. looking take username , password , authenticate user windows authentication login. after login, able authenticate them before (i.e. run query)

i found article:

http://geekswithblogs.net/manjunath.k/archive/2014/09/23/windows-authentication-in-asp.net-web-application.aspx

it appears wanna this:

var user = username; (username comes app) if(user.isinrole(windowsbuiltinrole.administrator)){     //user exists } 

but how authenticate password ? confused.