Usar recibos para comprobar compras de productos (HTML)
[ Este artículo está destinado a desarrolladores de Windows 8.x y Windows Phone 8.x que escriben aplicaciones de Windows en tiempo de ejecución. Si estás desarrollando para Windows 10, consulta la documentación más reciente
Cada transacción de la Tienda Windows que tiene como resultado una compra correcta del producto también puede devolver un recibo de la transacción. Este recibos proporcionan información sobre el producto enumerado y el coste abonado por el cliente.
El acceso a esta información resulta útil en aquellos casos en los que la aplicación debe comprobar que un usuario compró tu aplicación o ha realizado compras de productos desde la aplicación en la Tienda Windows. Por ejemplo, imagina un juego que ofrece contenido descargado. Si el usuario que compró el contenido quiere jugar en otro dispositivo, debes comprobar que ese usuario ya sea propietario del contenido. Pasos a seguir:
Solicitar un recibo
El espacio de nombres Windows.ApplicationModel.Store admite dos maneras de obtener un recibo: mediante el uso de CurrentApp.RequestProductPurchaseAsync | requestProductPurchaseAsync o CurrentApp.RequestAppPurchaseAsync | requestAppPurchaseAsync y el uso del parámetro includeReceipt, o llamando al método CurrentApp.GetAppReceiptAsync | getAppReceiptAsync. Un recibo de aplicación tiene la siguiente apariencia.
<Receipt Version="1.0" ReceiptDate="2012-08-30T23:10:05Z" CertificateId="b809e47cd0110a4db043b3f73e83acd917fe1336" ReceiptDeviceId="4e362949-acc3-fe3a-e71b-89893eb4f528">
<AppReceipt Id="8ffa256d-eca8-712a-7cf8-cbf5522df24b" AppId="55428GreenlakeApps.CurrentAppSimulatorEventTest_z7q3q7z11crfr" PurchaseDate="2012-06-04T23:07:24Z" LicenseType="Full" />
<ProductReceipt Id="6bbf4366-6fb2-8be8-7947-92fd5f683530" ProductId="Product1" PurchaseDate="2012-08-30T23:08:52Z" ExpirationDate="2012-09-02T23:08:49Z" ProductType="Durable" AppId="55428GreenlakeApps.CurrentAppSimulatorEventTest_z7q3q7z11crfr" />
<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
<SignedInfo>
<CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
<SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256" />
<Reference URI="">
<Transforms>
<Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" />
</Transforms>
<DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256" />
<DigestValue>cdiU06eD8X/w1aGCHeaGCG9w/kWZ8I099rw4mmPpvdU=</DigestValue>
</Reference>
</SignedInfo>
<SignatureValue>SjRIxS/2r2P6ZdgaR9bwUSa6ZItYYFpKLJZrnAa3zkMylbiWjh9oZGGng2p6/gtBHC2dSTZlLbqnysJjl7mQp/A3wKaIkzjyRXv3kxoVaSV0pkqiPt04cIfFTP0JZkE5QD/vYxiWjeyGp1dThEM2RV811sRWvmEs/hHhVxb32e8xCLtpALYx3a9lW51zRJJN0eNdPAvNoiCJlnogAoTToUQLHs72I1dECnSbeNPXiG7klpy5boKKMCZfnVXXkneWvVFtAA1h2sB7ll40LEHO4oYN6VzD+uKd76QOgGmsu9iGVyRvvmMtahvtL1/pxoxsTRedhKq6zrzCfT8qfh3C1w==</SignatureValue>
</Signature>
</Receipt>
Un recibo de producto tiene la siguiente apariencia.
<Receipt Version="1.0" ReceiptDate="2012-08-30T23:08:52Z" CertificateId="b809e47cd0110a4db043b3f73e83acd917fe1336" ReceiptDeviceId="4e362949-acc3-fe3a-e71b-89893eb4f528">
<ProductReceipt Id="6bbf4366-6fb2-8be8-7947-92fd5f683530" ProductId="Product1" PurchaseDate="2012-08-30T23:08:52Z" ExpirationDate="2012-09-02T23:08:49Z" ProductType="Durable" AppId="55428GreenlakeApps.CurrentAppSimulatorEventTest_z7q3q7z11crfr" />
<Signature xmlns="http://www.w3.org/2000/09/xmldsig#">
<SignedInfo>
<CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#" />
<SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256" />
<Reference URI="">
<Transforms>
<Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature" />
</Transforms>
<DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256" />
<DigestValue>Uvi8jkTYd3HtpMmAMpOm94fLeqmcQ2KCrV1XmSuY1xI=</DigestValue>
</Reference>
</SignedInfo>
<SignatureValue>TT5fDET1X9nBk9/yKEJAjVASKjall3gw8u9N5Uizx4/Le9RtJtv+E9XSMjrOXK/TDicidIPLBjTbcZylYZdGPkMvAIc3/1mdLMZYJc+EXG9IsE9L74LmJ0OqGH5WjGK/UexAXxVBWDtBbDI2JLOaBevYsyy+4hLOcTXDSUA4tXwPa2Bi+BRoUTdYE2mFW7ytOJNEs3jTiHrCK6JRvTyU9lGkNDMNx9loIr+mRks+BSf70KxPtE9XCpCvXyWa/Q1JaIyZI7llCH45Dn4SKFn6L/JBw8G8xSTrZ3sBYBKOnUDbSCfc8ucQX97EyivSPURvTyImmjpsXDm2LBaEgAMADg==</SignatureValue>
</Signature>
</Receipt>
Puedes usar cualquiera de estos ejemplos de recibo para probar tu código de validación.
Validar un recibo
Después de obtener un recibo, necesitas que tu sistema back-end (un servicio web o algo similar) lo valide. A continuación te mostramos un ejemplo de ese proceso de validación en .NET Framework.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Security.Cryptography;
using System.Security.Cryptography.X509Certificates;
using System.Xml;
using System.IO;
using System.Security.Cryptography.Xml;
using System.Net;
namespace ReceiptVerificationSample
{
public sealed class RSAPKCS1SHA256SignatureDescription : SignatureDescription
{
public RSAPKCS1SHA256SignatureDescription()
{
base.KeyAlgorithm = typeof(RSACryptoServiceProvider).FullName;
base.DigestAlgorithm = typeof(SHA256Managed).FullName;
base.FormatterAlgorithm = typeof(RSAPKCS1SignatureFormatter).FullName;
base.DeformatterAlgorithm = typeof(RSAPKCS1SignatureDeformatter).FullName;
}
public override AsymmetricSignatureDeformatter CreateDeformatter(AsymmetricAlgorithm key)
{
if (key == null)
{
throw new ArgumentNullException("key");
}
RSAPKCS1SignatureDeformatter deformatter = new RSAPKCS1SignatureDeformatter(key);
deformatter.SetHashAlgorithm("SHA256");
return deformatter;
}
public override AsymmetricSignatureFormatter CreateFormatter(AsymmetricAlgorithm key)
{
if (key == null)
{
throw new ArgumentNullException("key");
}
RSAPKCS1SignatureFormatter formatter = new RSAPKCS1SignatureFormatter(key);
formatter.SetHashAlgorithm("SHA256");
return formatter;
}
}
class Program
{
// Utility function to read the bytes from an HTTP response
private static int ReadResponseBytes(byte[] responseBuffer, Stream resStream)
{
int count = 0;
int numBytesRead = 0;
int numBytesToRead = responseBuffer.Length;
do
{
count = resStream.Read(responseBuffer, numBytesRead, numBytesToRead);
numBytesRead += count;
numBytesToRead -= count;
} while (count > 0);
return numBytesRead;
}
public static X509Certificate2 RetrieveCertificate(string certificateId)
{
const int MaxCertificateSize = 10000;
// We are attempting to retrieve the following url. The getAppReceiptAsync website at
// https://msdn.microsoft.com/en-us/library/windows/apps/windows.applicationmodel.store.currentapp.getappreceiptasync.aspx
// lists the following format for the certificate url.
String certificateUrl = String.Format("https://go.microsoft.com/fwlink/?LinkId=246509&cid={0}", certificateId);
// Make an HTTP GET request for the certificate
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(certificateUrl);
request.Method = "GET";
HttpWebResponse response = (HttpWebResponse)request.GetResponse();
// Retrieve the certificate out of the response stream
byte[] responseBuffer = new byte[MaxCertificateSize];
Stream resStream = response.GetResponseStream();
int bytesRead = ReadResponseBytes(responseBuffer, resStream);
if (bytesRead < 1)
{
//TODO: Handle error here
}
return new X509Certificate2(responseBuffer);
}
static bool ValidateXml(XmlDocument receipt, X509Certificate2 certificate)
{
// Create the signed XML object.
SignedXml sxml = new SignedXml(receipt);
// Get the XML Signature node and load it into the signed XML object.
XmlNode dsig = receipt.GetElementsByTagName("Signature", SignedXml.XmlDsigNamespaceUrl)[0];
if (dsig == null)
{
// If signature is not found return false
System.Console.WriteLine("Signature not found.");
return false;
}
sxml.LoadXml((XmlElement)dsig);
// Check the signature
bool isValid = sxml.CheckSignature(certificate, true);
return isValid;
}
static void Main(string[] args)
{
// .NET does not support SHA256-RSA2048 signature verification by default, so register this algorithm for verification
CryptoConfig.AddAlgorithm(typeof(RSAPKCS1SHA256SignatureDescription), "http://www.w3.org/2001/04/xmldsig-more#rsa-sha256");
// Load the receipt that needs to be verified as an XML document
XmlDocument xmlDoc = new XmlDocument();
xmlDoc.Load("..\\..\\receipt.xml");
// The certificateId attribute is present in the document root, retrieve it
XmlNode node = xmlDoc.DocumentElement;
string certificateId = node.Attributes["CertificateId"].Value;
// Retrieve the certificate from the official site.
// NOTE: For sake of performance, you would want to cache this certificate locally.
// Otherwise, every single call will incur the delay of certificate retrieval.
X509Certificate2 verificationCertificate = RetrieveCertificate(certificateId);
try
{
// Validate the receipt with the certificate retrieved earlier
bool isValid = ValidateXml(xmlDoc, verificationCertificate);
System.Console.WriteLine("Certificate valid: " + isValid);
}
catch (Exception ex)
{
System.Console.WriteLine(ex.ToString());
}
}
}
}