public override string ComputeSignature(string signatureBaseString, string consumerSecret)
    {
        var key       = PercentEncode(consumerSecret) + "&";
        var secretKey = new SecretKeySpec(key.GetBytes(), EncryptionMethods.HMACSHA1);

        using (Mac mac = new Mac(secretKey, signatureBaseString))
        {
            return(mac.AsBase64());
        }
    }