SignURL.cs

class Program
{
    static void Main(string[] args)
    {
        string secretCode = "9tGaq1zidmxJN8Pid6IMYhHFqAUwNbu";  // secret code
        var url = "https://example.com";

        // Variable declaration to form the signature URL 
        var query = "?page=4&access=rwd&"; // Add queries that you need.
        var nonce = Guid.NewGuid().ToString(); // random string - To prevent replay attacks.
        double timeStamp = DateTimeToUnixTimeStamp(DateTime.UtcNow); // current time as UNIX time stamp
        var expirationTime = "100"; // alive time of the token - This can be used to make the URL expire.
        var userId = 1; // User ID or user email


        string queryParameter = query + "nonce=" + nonce + "&user_id=" + userId + "&timestamp=" + timeStamp + "&expirationtime=" + expirationTime;

        string signature = SignURL(queryParameter.ToLower(), secretCode);
        string queryWithSignature = queryParameter.ToLower() + "&signature=" + signature;
        var signedUrl = url + queryWithSignature;
    }

    static string SignURL(string message, string secretcode)    
    {
        var encoding = new UTF8Encoding();
        var keyBytes = encoding.GetBytes(secretcode);
        var messageBytes = encoding.GetBytes(message);
        using (var hmacsha1 = new HMACSHA256(keyBytes))
        {
            var hashMessage = hmacsha1.ComputeHash(messageBytes);
            return Convert.ToBase64String(hashMessage);
        }
    }

    static double DateTimeToUnixTimeStamp(DateTime dateTime)
    {
        DateTime unixStart = new DateTime(1970, 1, 1, 0, 0, 0, 0, System.DateTimeKind.Utc);
        long unixTimeStampInTicks = (dateTime.ToUniversalTime() - unixStart).Ticks;
        return unixTimeStampInTicks / TimeSpan.TicksPerSecond;
    }
}