---
title: Generating a Promotional Offer Signature on the Server
framework: storekit
role: sampleCode
role_heading: Sample Code
path: storekit/generating-a-promotional-offer-signature-on-the-server
---

# Generating a Promotional Offer Signature on the Server

Generate a signature using your private key and lightweight cryptography libraries.

## Overview

Overview note: This sample code project is associated with WWDC 2019 session 305: Subscription Offers Best Practices. This sample code is a simple server written using JavaScript and Node.js. It demonstrates how to generate a signature for promotional offers. The sample demonstrates: Receiving a request. Generating a cryptographic signature using your private key. Sending back a response with the signature. All of the work is done in routes/index.js. You set up environment variables for your key ID and your private key in the start-server file. Configure the Sample Code Project Install the latest stable version of Node.js. Open Terminal.app and navigate to the sample code directory. Run npm install from the command line, and make sure it completes successfully. The start-server file contains a key ID and private key PEM string. The values provided in the sample are for example purposes only and will not generate signatures that are valid for your apps. You can optionally open start-server with a text editor and replace the example key ID and private key PEM string with your own key ID and private key PEM string that you received from App Store Connect. Run a Test on Your Local Server To test the code on your local machine, from the command line: Navigate to the sample code source folder and run ./start-server from the command line. The server is now running locally and is ready to accept connections on port 3000. Open another terminal window and use the curl command to send a request. This example command uses the same data listed in the JSON example below: curl -X GET -H "Content-type: application/json" -d '{"appBundleID": "com.example.yourapp", "productIdentifier": "com.example.yoursubscription", "offerID": "your_offer_id", "applicationUsername": "8E3DC5F16E13537ADB45FB0F980ACDB6B55839870DBCE7E346E1826F5B0296CA"}' http://127.0.0.1:3000/offer You will get a response that includes the signature. Send a Request To run this sample code, send a request to this URL: GET http://<yourdomain>/offer, where <yourdomain> is the domain name or IP address of the server this sample code is running on. The request must have a Content-type header of application/json, and JSON body data with the following format: {     "appBundleID": "com.example.yourapp",     "productIdentifier": "com.example.yoursubscription",     "offerID": "your_offer_id",     "applicationUsername": "8E3DC5F16E13537ADB45FB0F980ACDB6B55839870DBCE7E346E1826F5B0296CA" }

## See Also

### Promotional offers

- [Setting up promotional offers](storekit/setting-up-promotional-offers.md)
- [Implementing promotional offers in your app](storekit/implementing-promotional-offers-in-your-app.md)
- [Generating a signature for promotional offers](storekit/generating-a-signature-for-promotional-offers.md)
- [SKPaymentDiscount](storekit/skpaymentdiscount.md)