public void AddHeaderParameter(string key, string value)
    {
        var comparison = StringComparison.InvariantCultureIgnoreCase;

        if (key.StartsWith("content-", comparison) &&
            !string.IsNullOrEmpty(value) &&
            !BodyParameters.ContainsKey(key))
        {
            BodyParameters.Add(key, value);
        }
        HeaderParameters[key] = value;
    }