using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var allChar = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";  

        var random = new Random();  

        var resultToken = new string(  

       Enumerable.Repeat(allChar , 8)  

       .Select(token => token[random.Next(token.Length)]).ToArray());   

​

       string authToken = resultToken.ToString();  

        Console.WriteLine("authToken:" + authToken);

    }

}