Hoe to do intranet Single sign on with Active directory(OR LDAP) through kerboroes authentication

using System.DirectoryServices;

public static string IsUserValid() 
{
    string szReturnMsg="";
    try
    {
        LdapConnection ldp = new LdapConnection
        		(new LdapDirectoryIdentifier((string)null, false, false));
        NetworkCredential userInfo = new NetworkCredential(Environment.UserName, 
                               "UserPassword", Environment.UserDomainName);
        ldp.Credential = userInfo;
        ldp.AuthType = AuthType.Negotiate;
        ldp.Bind(userInfo);
        szReturnMsg="User Successfully validated!"
    }
    catch (LdapException ex)
    {
        szReturnMsg = ex.Message();
    }
    return szReturnMsg;
}