How to set single sign on asp.net c#?

i want to set single sign on to application using system user name.

 

my comuter name is raja and user name is admin

 

i use many codes

 

string Domain = System.Net.NetworkInformation.IPGlobalProperties.GetIPGlobalProperties().DomainName;

string Host = System.Net.Dns.GetHostName();

string USER = System.Security.Principal.WindowsIdentity.GetCurrent().Name;

System.Net.IPHostEntry host = System.Net.Dns.GetHostEntry(System.Net.Dns.GetHostName());

all is working in my local machine fine but i host the application to server the code  is does not get the username of local system this is get only hosted name if i host the application name of 'test' the codes get only test.

i want local system name

 

local system name is 'rjk'

application login to without ask username and password

all of the user have the rjk keyword so

if(LOGIN_USER.Contains("rjk"))
{
//successfully login
}

 how to do it.