ExpireTimeValidation.cs

var isValidSignatureKey = SignatureValidation(query, secretCode, signature);

var expireTime = Convert.ToInt32(filterContext.HttpContext.Request.Query["expiretime"]);
DateTime timeStampDateTime = DateTimeHelper.UnixTimeStampToDateTime(Convert.ToDouble(filterContext.HttpContext.Request.Query["timestamp"]));
bool urlExpiryTime = DateTime.UtcNow > timeStampDateTime ? DateTime.UtcNow - timeStampDateTime <= TimeSpan.FromSeconds(expireTime) : false;               
if (isValidSignatureKey && urlExpiryTime && !string.IsNullOrEmpty(nonce))
{
    return true;
}