Azure DocumentDB: Compute Signature

docdb_signature.cs

public static string GetSignature(string masterKey, string resourceId, string resourceType, string xDate = null, string date = null)
{
  if (string.IsNullOrEmpty(xDate) && string.IsNullOrEmpty(date))
  {
   throw new ArgumentException("Either xDate or date must be provided.");
  }

  const string AuthorizationFormat = "type={0}&ver={1}&sig={2}";
  const string MasterToken = "master";
  const string TokenVersion = "1.0";

  var masterKeyBytes = Convert.FromBase64String(masterKey);
  var hmacSha256 = new HMACSHA256(masterKeyBytes);
  var resourceIdInput = resourceId ?? string.Empty;
  var resourceTypeInput = resourceType ?? string.Empty;

  if (string.IsNullOrEmpty(xDate)) {
    date.ToLowerInvariant();
  } else {
    date = string.Empty;
  }

  var payLoad = string.Format(CultureInfo.InvariantCulture,
  "{0}\n{1}\n{2}\n{3}\n{4}\n",
  "GET".ToLowerInvariant(),
  resourceTypeInput.ToLowerInvariant(),
  resourceIdInput.ToLowerInvariant(),
  (xDate ?? string.Empty).ToLowerInvariant(),
  date);
  var hashPayLoad = hmacSha256.ComputeHash(Encoding.UTF8.GetBytes(payLoad));
  var authorizationToken = Convert.ToBase64String(hashPayLoad);

  return System.Web.HttpUtility.UrlEncode(string.Format(
  CultureInfo.InvariantCulture,
  AuthorizationFormat,
  MasterToken,
  TokenVersion,
  authorizationToken));
}