Is there a tutorial on how to implement Google Authenticator in .NET apps?

The question asked for a tutorial which the other answers I don't feel cover,

one can be found at:

http://www.codeproject.com/Articles/403355/Implementing-Two-Factor-Authentication-in-ASP-NET

The tutorial was written by Rick Bassham and covers information on:

"What is Two Factor Authentication" "What is Google Authenticator" "How does it work"

It then explains how to implement code for:

"Counter Based One Time Password Generation" "Time Based One Time Password Generation"

And gives a full tutorial using Visual Studio 2010 under:

"How do I put it to use"

You could run this simple Console App to understand how to verify the one time token code. Note that we need to install library Otp.Net from Nuget package first.

static string secretKey = "JBSWY3DPEHPK3PXP"; //add this key to your Google Authenticator app  

private static void Main(string[] args)
{
        var bytes = Base32Encoding.ToBytes(secretKey);

        var totp = new Totp(bytes);

        while (true)
        {
            Console.Write("Enter your code from Google Authenticator app: ");
            string userCode = Console.ReadLine();

            //Generate one time token code
            string tokenInApp = totp.ComputeTotp();
            int remainingSeconds = totp.RemainingSeconds();

            if (userCode.Equals(tokenInApp)
                && remainingSeconds > 0)
            {
                Console.WriteLine("Success!");
            }
            else
            {
                Console.WriteLine("Failed. Try again!");
            }
        }
}