offsite.cs

 public class EWayOffsitePaymentSettings : IPaymentSettings
    {
        public string PaymentType
        {
            get { return "Sale"; }
            set { }
        }

        public string[] ProcessorCreditCards
        {
            get { return new string[] { }; }
            set { }
        }
    }
    
     public partial class paymentresult : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            EWayOffsiteGateway.ConfirmPayment(Request.Params["AccessPaymentCode"]);            
        }
    }

    public class EWayOffsitePaymentProvider : PaymentProcessorProviderBase, IOffsitePaymentProcessorProvider, IPaymentProcessorProvider        
    {
        public IPaymentResponse SubmitTransaction(IPaymentRequest data)
        {
            return Sale(data);
        }

        public IPaymentResponse Sale(IPaymentRequest data)
        {
            return new PaymentResponse
            {
                OrderNumber = data.OrderNumber,
                GatewayRedirectUrl = EWayOffsiteGateway.Process(data),
                GatewayRedirectUrlPostValues = new System.Collections.Specialized.NameValueCollection(),
                IsOffsitePayment = true
            };
        }

        public IPaymentResponse HandleOffsiteNotification(int orderNumber, HttpRequest request, Telerik.Sitefinity.Ecommerce.Orders.Model.PaymentMethod paymentMethod)
        {
            return new PaymentResponse
            {
                IsOffsitePayment = true
            };
        }

        public IPaymentResponse HandleOffsiteReturn(int orderNumber, HttpRequest request, Telerik.Sitefinity.Ecommerce.Orders.Model.PaymentMethod paymentMethod)
        {
            IPaymentResponse paymentResponse = new PaymentResponse
            {
                IsOffsitePayment = true
            };

            paymentResponse.IsSuccess = EWayOffsiteGateway.ConfirmPayment(request.Params["AccessPaymentCode"]);

            //work around for a bug in the eway payment provider?  makes querystrings lowercase which is very bad
            request.Params.AsDynamic().IsReadOnly = false; 
            request.Params["landingUrl"] = Compress(string.Format("http://{0}/store/checkout?step=confirmation&steps=3", request.Url.Authority));

            return paymentResponse;
        }

        internal static string Compress(string plainTextString)
        {
            byte[] bytes = System.Text.Encoding.Unicode.GetBytes(plainTextString);
            string result;
            using (System.IO.MemoryStream memoryStream = new System.IO.MemoryStream(bytes))
            {
                using (System.IO.MemoryStream memoryStream2 = new System.IO.MemoryStream())
                {
                    using (GZipStream gZipStream = new GZipStream(memoryStream2, CompressionMode.Compress))
                    {
                        memoryStream.CopyTo(gZipStream);
                    }
                    result = System.Convert.ToBase64String(memoryStream2.ToArray());
                }
            }
            return result;
        }
        
         #region NotImplemented
        public IPaymentResponse AuthVoidCapture(IPaymentRequest data)
        {
            throw new NotImplementedException();
        }

        public IPaymentResponse Authorize(IPaymentRequest data)
        {
            throw new NotImplementedException();
        }

        public IPaymentResponse Capture(IPaymentRequest data, string originalTransactionID)
        {
            throw new NotImplementedException();
        }

        public IPaymentResponse Credit(IPaymentRequest data)
        {
            throw new NotImplementedException();
        }

        public IPaymentResponse PerformValidations(IPaymentRequest data, bool avsAddress, bool avsZip, bool csc)
        {
            throw new NotImplementedException();
        }      

        public IPaymentResponse TestConnection(IPaymentRequest data)
        {
            throw new NotImplementedException();
        }

        public IPaymentResponse Void(IPaymentRequest data, string originalTransactionID)
        {
            throw new NotImplementedException();
        }
        #endregion
    }
    
    
    
     public static class EWayOffsiteGateway
    {
        private static string _gateway = "https://nz.ewaygateway.com";
        public static string Process(IPaymentRequest data)
        {
            TransactionRequest result = null;
            try
            {
                var client = new System.Net.Http.HttpClient();
                client.BaseAddress = new Uri(_gateway);
                
                var parameters = new Dictionary<string, string>() {
                    { "CustomerID", ConfigurationManager.AppSettings["EWayCustomerId"] },  
                    { "UserName", ConfigurationManager.AppSettings["EWayUsername"]  },     
                    { "CompanyName", ConfigurationManager.AppSettings["CompanyName"]  },

                    { "Amount", data.Amount.ToString("F2") },
                    { "Currency", data.CurrencyCode },

                    //Customer Details (customer is null??)
                    { "CustomerFirstName", data.BillingFirstName },
                    { "CustomLastName", data.BillingLastName },   
                    { "CustomerEmail", data.CustomerEmail },

                    //Billing Address Details
                    { "CustomerAddress", data.BillingStreet},
                    { "CustomerCity", data.BillingCity},
                    { "CustomerState", data.BillingState },
                    { "CustomerPostCode", data.BillingZip },
                    { "CustomerCountry", data.BillingCountry },
                    { "ModifiableCustomerDetails", "false" },
                    
                    { "ReturnURL", data.GatewayRedirectSuccessUrl  }, 
                    { "CancelURL", data.GatewayRedirectCancelUrl }, 
                    { "MerchantReference", data.OrderID.ToString() },                 
                };

                HttpQueryString queryString = new HttpQueryString();
                foreach (string key in parameters.Keys)
                {
                    queryString.Add(key, parameters[key]);
                }

                var response = client.PostAsync(queryString.MakeQueryString(new Uri("/Request/", UriKind.Relative)), null).Result;
                response.EnsureSuccessStatusCode();

                var xmlMediaTypeFormatter = new XmlMediaTypeFormatter();
                xmlMediaTypeFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
                xmlMediaTypeFormatter.UseXmlSerializer = true;
                result = response.Content.ReadAsAsync<TransactionRequest>(new[] { xmlMediaTypeFormatter }).Result;

                if (!"True".Equals(result.Result, StringComparison.OrdinalIgnoreCase))
                {
                    HttpContext.Current.Response.Redirect("/payment-failure");
                }
            }
            catch (Exception e)
            {
                //todo log error
                Enlighten.Net.ErrorHandler.ErrorHandlerFactory.HandleError(e);
                HttpContext.Current.Response.Redirect("/payment-failure");
            }
            
            return result.URI;            
        }

        public static bool ConfirmPayment(string accessPaymentCode)
        {
            var client = new System.Net.Http.HttpClient();
            client.BaseAddress = new Uri(_gateway);

            var parameters = new Dictionary<string, string>() {
                { "CustomerID", ConfigurationManager.AppSettings["EWayCustomerId"] },
                { "UserName", ConfigurationManager.AppSettings["EWayUsername"] },   
                { "AccessPaymentCode", accessPaymentCode }                
            };

            HttpQueryString queryString = new HttpQueryString();
            foreach (string key in parameters.Keys)
            {
                queryString.Add(key, parameters[key]);
            }

            var response = client.PostAsync(queryString.MakeQueryString(new Uri("/Result/", UriKind.Relative)), null).Result;
            response.EnsureSuccessStatusCode();

            var xmlMediaTypeFormatter = new XmlMediaTypeFormatter();
            xmlMediaTypeFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
            xmlMediaTypeFormatter.UseXmlSerializer = true;
            var result = response.Content.ReadAsAsync<TransactionResponse>(new[] { xmlMediaTypeFormatter }).Result;

            return result.ResponseCode == "00";           
        }
    }