using System.Security.Cryptography;

	public string PHPMD5(string text)
	     {
            var md5 = new MD5CryptoServiceProvider();
            byte[] bytesText = Encoding.UTF8.GetBytes(text.ToLower());
            byte[] bytesMD5Text = md5.ComputeHash(bytesText);
            StringBuilder sb = new StringBuilder();
            foreach (var b in bytesMD5Text)
            {
                sb.Append(b.ToString("x2").ToLower());
            }
            return sb.ToString();
        }

		using (HttpClient client = new HttpClient())
            {
                try
                {
                    client.DefaultRequestHeaders.Add("account", account);                   
                    client.DefaultRequestHeaders.Add("sign", sign);
                    client.DefaultRequestHeaders.Add("timestamp", timestamp);
                    client.Timeout = TimeSpan.FromSeconds(30);
                    HttpResponseMessage response = await client.GetAsync(url);
                    string responseBody = await response.Content.ReadAsStringAsync();
                    Console.WriteLine(responseBody);
                }
                catch (HttpRequestException ex)
                {
                    Console.WriteLine("Message :{0} ", ex.Message);
                }
            }