PayPal with ASP.NET MVC

http://www.superstarcoders.com/blogs/posts/paypal-with-asp-net-mvc.aspx

public class CartController : Controller
{
   public ActionResult Index()
   {
      return View();
   }

   public ActionResult Pay()
   {
      PayPalRedirect redirect = PayPal.ExpressCheckout(new PayPalOrder { Amount = 50 });

      Session["token"] = redirect.Token;

      return new RedirectResult(redirect.Url);
   }
}

Here is the PayPal API code that you can include in your solution or a separate library:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Collections.Specialized;
using System.Net;
using System.IO;
using System.Globalization;

public class PayPal
{
   public static PayPalRedirect ExpressCheckout(PayPalOrder order)
   {
      NameValueCollection values = new NameValueCollection();

      values["METHOD"] = "SetExpressCheckout";
      values["RETURNURL"] = PayPalSettings.ReturnUrl;
      values["CANCELURL"] = PayPalSettings.CancelUrl;
      values["AMT"] = "";
      values["PAYMENTACTION"] = "Sale";
      values["CURRENCYCODE"] = "GBP";
      values["BUTTONSOURCE"] = "PP-ECWizard";
      values["USER"] = PayPalSettings.Username;
      values["PWD"] = PayPalSettings.Password;
      values["SIGNATURE"] = PayPalSettings.Signature;
      values["SUBJECT"] = "";
      values["VERSION"] = "2.3";
      values["AMT"] = order.Amount.ToString(CultureInfo.InvariantCulture);

      values = Submit(values);

      string ack = values["ACK"].ToLower();

      if (ack == "success" || ack == "successwithwarning")
      {
         return new PayPalRedirect
         {
            Token = values["TOKEN"],
            Url = String.Format("https://{0}/cgi-bin/webscr?cmd=_express-checkout&token={1}",
               PayPalSettings.CgiDomain, values["TOKEN"])
         };
      }
      else
      {
         throw new Exception(values["L_LONGMESSAGE0"]);
      }
   }

   private static NameValueCollection Submit(NameValueCollection values)
   {
      string data = String.Join("&", values.Cast<string>()
        .Select(key => String.Format("{0}={1}", key, HttpUtility.UrlEncode(values[key]))));

      HttpWebRequest request = (HttpWebRequest)WebRequest.Create(
         String.Format("https://{0}/nvp",PayPalSettings.ApiDomain));
      
      request.Method = "POST";
      request.ContentLength = data.Length;

      using (StreamWriter writer = new StreamWriter(request.GetRequestStream()))
      {
         writer.Write(data);
      }

      using (StreamReader reader = new StreamReader(request.GetResponse().GetResponseStream()))
      {
         return HttpUtility.ParseQueryString(reader.ReadToEnd());
      }
   }
}