How to get current PC Username?

Question

I want to implement single sign on.

 

I get the user name of local pc using many codes(Given below)

 

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

string fff= System.Environment.GetEnvironmentVariable("UserName");

 

string ff=Request.LogonUserIdentity.Name.Substring(Request.LogonUserIdentity.Name.LastIndexOf(@"\") + 1);

 
string userName = System.Security.Principal.WindowsIdentity.GetCurrent().Name;
     
These codes are get the pc user name but i after host to server these codes are get only server pc name not get local pc name.

string fff= System.Environment.GetEnvironmentVariable("UserName");

the above code i used my local code these is get the local pc name after 

i host my application this is get the user name of LOCAL PC Computer name not get user name of local PC 

How to fix it.