Support Amazon purchase verification (#29)

* Support for verifying Amazon receipts

Author: Justin Page

README.md

@@ -25,6 +25,7 @@ var payment = {
 	packageName: 'my.app',
 	secret: 'password',
 	subscription: true,	// optional, if google play subscription
+	userId: 'user id', // required, if amazon
 	devToken: 'developer id' // required, if roku
 };
 
@@ -38,6 +39,42 @@ the next chapter for more information on the format.
 
 ## Supported platforms
 
+### Amazon 
+
+**The payment object**
+
+The receipt string represents the transaction returned from a channel or product
+purchase.
+
+A Shared secret and user ID is required.
+
+**The response**
+
+The response passed back to your callback will also be Amazon specific. The entire parsed receipt
+will be in the result object:
+
+```json
+{
+	"receipt": {
+		"betaProduct": false,
+		"cancelDate": null,
+		"parentProductId": null,
+		"productId": "com.amazon.iapsamplev2.gold_medal",
+		"productType": "CONSUMABLE",
+		"purchaseDate": 1399070221749,
+		"quantity": 1,
+		"receiptId": "wE1EG1gsEZI9q9UnI5YoZ2OxeoVKPdR5bvPMqyKQq5Y=:1:11",
+		"renewalDate": null,
+		"term": null,
+		"termSku": null,
+		"testTransaction": false
+	},
+	"transactionId": "wE1EG1gsEZI9q9UnI5YoZ2OxeoVKPdR5bvPMqyKQq5Y=:1:11",
+	"productId": "com.amazon.iapsamplev2.gold_medal",
+	"platform": "amazon"
+}
+```
+
 ### Apple
 
 **The payment object**
@@ -212,6 +249,15 @@ MIT
 
 ## References
 
+### Amazon References
+**Code Inspiration**
+
+ * https://github.com/may215/amazon_iap 
+
+**API Reference**
+
+ * https://developer.amazon.com/public/apis/earn/in-app-purchasing/docs-v2/verifying-receipts-in-iap	
+
 ### Apple References
 **Code Inspiration**
 
@@ -221,7 +267,6 @@ MIT
 
  * 	https://developer.apple.com/library/ios/releasenotes/General/ValidateAppStoreReceipt/Chapters/ValidateRemotely.html
 
-
 ### Google Play References
 **Code Inspiration**
 

bin/verify-amazon.js

@@ -0,0 +1,22 @@
+#!/usr/bin/env node
+
+var argv = require('minimist')(process.argv.slice(2), { string: ['secret', 'userId', 'receipt'] });
+
+if (argv.help) {
+	console.log('Usage: ./verfiy.js --secret=\'shared-secret\' --userId=\'amazon-user\' --receipt=\'receipt-data\'');
+	process.exit(1);
+}
+
+var iap = require('../index.js');
+
+var platform = 'amazon';
+var payment = argv;
+
+iap.verifyPayment(platform, payment, function (error, result) {
+	if (error) {
+		return console.log(error);
+	}
+
+	console.log('Verified:');
+	console.log(JSON.stringify(result, null, '\t'));
+});

index.js

@@ -1,4 +1,5 @@
 var platforms = {
+	amazon: require('./lib/amazon'),
 	apple: require('./lib/apple'),
 	google: require('./lib/google'),
 	roku: require('./lib/roku')

lib/amazon/index.js

@@ -0,0 +1,60 @@
+var assert = require('assert');
+var https = require('../https');
+
+var apiUrl = {
+	production: 'https://appstore-sdk.amazon.com/version/1.0/verifyReceiptId/developer/'
+};
+
+exports.verifyPayment = function (payment, cb) {
+	try {
+		assert.equal(typeof payment.secret, 'string', 'Shared secret must be a string');
+		assert.equal(typeof payment.userId, 'string', 'User ID must be a string');
+		assert.equal(typeof payment.receipt, 'string', 'Receipt must be a string');
+	} catch (error) {
+		return process.nextTick(function () {
+			cb(error);
+		});
+	}
+
+	var requestUrl = apiUrl.production + payment.secret + '/user/' + payment.userId + '/receiptId/' + payment.receipt;
+
+	https.get(requestUrl, null, function (error, res, resultString) {
+		if (error) {
+			return cb(error);
+		}
+
+		var resultObject = null;
+
+		try {
+			resultObject = JSON.parse(resultString);
+		} catch (error) {
+			return cb(error);
+		}
+
+		if (res.statusCode === 400) {
+			return cb(new Error('receiptId is invalid, or no transaction was found for this receiptId'));
+		}
+
+		if (res.statusCode === 496 ) {
+			return cb(new Error('Invalid sharedSecret'));
+		}
+
+		if (res.statusCode === 497) {
+			return cb(new Error('Invalid User ID'));
+		}
+
+		if (res.statusCode === 500) {
+			return cb(new Error('There was an Internal Servor Error'));
+		}
+
+		if (res.statusCode !== 200) {
+			return cb(new Error('Unknown operation exception'));
+		}
+
+		cb(null, {
+			receipt: resultObject,
+			transactionId: resultObject.receiptId,
+			productId: resultObject.productId
+		});
+	});
+};