title: I need to Hash a message with a key using Sha256 on windows 8
body: <p>So in the old days I used to use System.Security.Cryptography which is not available in windows 8. what i found in windows 8 was windows.security
  but i didn't find any examples on how to use Sha256 with a key.
  This is the old code that I used with System.Security.Cryptography</p>
  
  <pre><code>        string appID = "appid";
          string key = "password";
          var hmacsha256 = new HMACSHA256(Encoding.Default.GetBytes(key));
          hmacsha256.ComputeHash(Encoding.Default.GetBytes(appID));
          string k = "";
          foreach (byte test in hmacsha256.Hash)
          {
              k += test.ToString("X2");
          }
  </code></pre>