using System;

using System.Text;

using System.Collections.Generic;

using System.Linq;

using System.Security.Cryptography;

​

public class Program

{

    /// <summary>

    /// Returns a cryptographic hash of the given input.

    /// </summary>

    private static byte[] Sha256Digest(string input, Encoding encoding)

    {

        var sha256 = SHA256.Create();

        var inputBytes = encoding.GetBytes(input);

        return sha256.ComputeHash(inputBytes);

    }

    /// <summary>

    /// Generates a hash based on request payload as per https://tools.ietf.org/id/draft-eaton-oauth-bodyhash-00.html.

    /// "If the request does not have an entity body, the hash should be taken over the empty string".

    /// </summary>

    internal static string GetBodyHash(string payload, Encoding encoding) => Convert.ToBase64String(Sha256Digest(payload ?? string.Empty, encoding));

    public static void Main()

    {

        Console.WriteLine(GetBodyHash(string.Empty, Encoding.Default));

    }

}