Just copy/paste the code :)

Please change the function:

/// <summary>
/// Normalizes the request parameters according to the spec
/// </summary>
/// <param name="parameters">The list of parameters already sorted</param>
/// <returns>a string representing the normalized parameters</returns>
protected string NormalizeRequestParameters(IList<QueryParameter> parameters)
{
  StringBuilder sb = new StringBuilder();
  QueryParameter p = null;
  for (int i = 0; i < parameters.Count; i++)
  {
    p = parameters[i];
    sb.AppendFormat("{0}={1}", p.Name, p.Value);

    if (i < parameters.Count - 1)
    {
      sb.Append("&");
    }
  }

  return sb.ToString();
}

To this one:

/// <summary>
/// Normalizes the request parameters according to the spec
/// </summary>
/// <param name="parameters">The list of parameters already sorted</param>
/// <returns>a string representing the normalized parameters</returns>
protected string NormalizeRequestParameters(IList<QueryParameter> parameters)
{
  StringBuilder sb = new StringBuilder();
  QueryParameter p = null;
  for (int i = 0; i < parameters.Count; i++)
  {
    p = parameters[i];
    sb.AppendFormat("{0}={1}", UrlEncode(p.Name), UrlEncode(p.Value));

    if (i < parameters.Count - 1)
    {
      sb.Append("&");
    }
  }

  return sb.ToString();
}