How to save username in global variable asp

I have online exam system I want to save username in global variable or any other thing that just can save it.
I want this username for get and set data on SQL database.
I'm using a global variable in class but it replace in every login.
any way to save username foreach user?

 public class GVar
{
    public static string user
    {
        get; set;
    }
    public static string mail
    {
        get;
        set;
    }
    public static string melli
    {
        get;
        set;
    }
    public static bool go
    {
        get;
        set;
    }

    public static System.Threading.Thread thread { get; set; }
}