Generating an SSO token for integration with Tenderapp.com using c# / .NET

SSOIntegrationWithTender.cs

//Third party dependencies: Newtonsoft JSON Library
public class TenderHelpService
    {
        public string SiteKey
        {
            get { return "your_site_key"; }
        }

        public string ApiKey
        {
            get { return "your_api_key"; }
        }
        
        public string BuildSSOToken(User user)
        {
            //user is simply an object that stores some information about your user
            var userDetails = JsonConvert.SerializeObject(
                new
                {
                    name = user.UserName
                    ,email = user.Email
                    ,unique_id = user.Id
                    ,trusted = true
                    ,expires = DateTime.Now.ToUniversalTime().AddHours(15).ToString("ddd MMM dd hh:mm:ss UTC yyyy")
                }
            );

            string initVector = "OpenSSL for Ruby";

            byte[] initVectorBytes = Encoding.UTF8.GetBytes(initVector);
            byte[] keyBytesLong;
            using (SHA1CryptoServiceProvider sha = new SHA1CryptoServiceProvider())
            {
                keyBytesLong = sha.ComputeHash(Encoding.UTF8.GetBytes(ApiKey + SiteKey));
            }
            byte[] keyBytes = new byte[16];
            Array.Copy(keyBytesLong, keyBytes, 16);

            string ud = JsonConvert.SerializeObject(userDetails).Replace(@"\", "");
            ud = ud.Substring(1, ud.Length - 2);

            byte[] textBytes = Encoding.UTF8.GetBytes(ud);
            for (int i = 0; i < 16; i++)
            {
                textBytes[i] ^= initVectorBytes[i];
            }

            // Encrypt the string to an array of bytes
            byte[] encrypted = aes(textBytes, keyBytes, initVectorBytes);
            string token = Convert.ToBase64String(encrypted);

            token = token.Replace("+", "-").Replace("/", "_").Replace(Environment.NewLine, "");
            token = (token.Substring(token.Length - 1, 1) == "=") ? token.Substring(0, token.Length - 2) : token;

            return token;
        }

        static byte[] aes(byte[] textBytes, byte[] Key, byte[] IV)
        {
            // Declare the stream used to encrypt to an in memory
            // array of bytes and the RijndaelManaged object
            // used to encrypt the data.
            using (MemoryStream msEncrypt = new MemoryStream())
            using (RijndaelManaged aesAlg = new RijndaelManaged())
            {
                // Provide the RijndaelManaged object with the specified key and IV.
                aesAlg.Mode = CipherMode.CBC;
                aesAlg.Padding = PaddingMode.PKCS7;
                aesAlg.KeySize = 128;
                aesAlg.BlockSize = 128;
                aesAlg.Key = Key;
                aesAlg.IV = IV;
                // Create an encrytor to perform the stream transform.
                ICryptoTransform encryptor = aesAlg.CreateEncryptor();

                // Create the streams used for encryption.
                using (CryptoStream csEncrypt = new CryptoStream(msEncrypt, encryptor, CryptoStreamMode.Write))
                {
                    csEncrypt.Write(textBytes, 0, textBytes.Length);
                    csEncrypt.FlushFinalBlock();
                }

                byte[] encrypted = msEncrypt.ToArray();
                // Return the encrypted bytes from the memory stream.
                return encrypted;
            }
        }   
    }