App Store Server Notifications is a server-to-server service that notifies you in real-time when the status of in-app purchases and refunds changes. Use the data in the notifications to update your user-account database, and to monitor and respond to in-app purchase refunds.

My main goal is to get originalTransactionId from the notification data then when a subscription gets Expired or Refunded, will downgrade the user subscription status.

FYI when user purchases we verify Apple’s receipt and we save originalTransactionId in our database. So each user have originalTransactionId and we can find the user with this originalTransactionId. You can read more about this here Auto-renewable subscriptions with SwiftUI

Make sure you set your app store notification URL on the AppStoreConnect. Choose Version 2 Notifications.

App Store Server Notifications V2 with JWT, PHP and Laravel

For this article, our production server URL looks like sminrana.com/jwt.php. You can get whatever Apple sends you and write a log in your server, if you are interested. 

$appleData = file_get_contents('php://input');
$file = fopen(
    "/var/www/html/appstore_prod.log", "a"
);
fwrite($file, $appleData);
fclose($file);

Each data will look like this, call it signedPayload.

App Store Server Notifications V2 with JWT, PHP and Laravel

The signedPayload object is a JWS representation. To get the transaction and subscription renewal details from the notification payload, process the signedPayload as follows:

  1. Parse signedPayload to identify the JWS header, payload, and signature representations.
  2. Base64 URL-decode the payload to get the responseBodyV2DecodedPayload. The decoded payload contains the notificationType , subtype, other notification metadata, and a data object.
  3. The data object contains a signedTransactionInfo (JWSTransaction) and depending on the notification type, a signedRenewalInfo (JWSRenewalInfo). Parse and Base64 URL-decode these signed JWS representations to get transaction and subscription renewal details.

Each of the signed JWS representations, signedPayload, signedTransactionInfo, and signedRenewalInfo, have a JWS signature that you can validate on your server. Use the algorithm specified in the header’s alg parameter to validate the signature. For more information about validating signatures, see the JSON Web Signature (JWS) IETF RFC 7515 specification.

Hopefully, you are already getting this data. Now let’s get originalTransactionId from this. We will do this without any 3rd party library first to understand the process.

Very first thing, I will download the Apple root certificate and make .PEM file from it.

Download the certificate https://www.apple.com/certificateauthority/AppleRootCA-G3.cer

Get .PEM file from it, on your Mac Terminal

openssl x509 -in AppleRootCA-G3.cer -out apple_root.pem

For testing purposes, I’m loading apple_root.pem and my signedPayload from a file called notification.json (replace it with file_get_contents(‘php://input’);) and then decoding the signedPayload. signedPayload has three parts, separated by .(dot), line 13.

First part is the header, the Second part is the body (payload) and the Third part is the signature. The header has an algorithm and x5c, x5c has three elements. Certificate, intermediate certificate, and root certificate. We can verify the certificate in two steps. Once the verification is completed we know we have signedPayload from Apple.

Finally, decode the payload again and get the originalTransactionId from line 56 to 65.

Without any 3rd party library(not recommended). 

<?php

ini_set('display_errors', 1);
error_reporting(E_ALL);

// Download the certificate -> https://www.apple.com/certificateauthority/AppleRootCA-G3.cer
// Convert it to .PEM file, run on macOS terminal ->  ```bash openssl x509 -in AppleRootCA-G3.cer -out apple_root.pem```

$pem = file_get_contents('apple_root.pem');
$data = file_get_contents('notification.json'); // replace with file_get_contents('php://input');
$json = json_decode($data);

$header_payload_secret = explode('.', $json->signedPayload);

//------------------------------------------
// Header
//------------------------------------------
$header = json_decode(base64_decode($header_payload_secret[0]));
$algorithm = $header->alg;
$x5c = $header->x5c; // array
$certificate = $x5c[0];
$intermediate_certificate = $x5c[1];
$root_certificate = $x5c[2];

$certificate =
      "-----BEGIN CERTIFICATE-----\n"
    . $certificate
    . "\n-----END CERTIFICATE-----";

$intermediate_certificate =
      "-----BEGIN CERTIFICATE-----\n"
    . $intermediate_certificate
    . "\n-----END CERTIFICATE-----";

$root_certificate =
      "-----BEGIN CERTIFICATE-----\n"
    . $root_certificate
    . "\n-----END CERTIFICATE-----";

//------------------------------------------
// Verify the notification request   
//------------------------------------------
if (openssl_x509_verify($intermediate_certificate, $root_certificate) != 1){ 
    echo 'Intermediate and Root certificate do not match';
    exit;
}

// Verify again with Apple root certificate
if (openssl_x509_verify($root_certificate, $pem) == 1){
    //------------------------------------------
    // Payload
    //------------------------------------------
    // https://developer.apple.com/documentation/appstoreservernotifications/notificationtype
    // https://developer.apple.com/documentation/appstoreservernotifications/subtype
    $payload = json_decode(base64_decode($header_payload_secret[1]));
    $notificationType = $payload->notificationType;
    $subtype = $payload->subtype;

    if ($notificationType == "EXPIRED" || $notificationType == "REFUND") {
        $transactionInfo = $payload->data->signedTransactionInfo;
        $ti = explode('.', $transactionInfo);
        
        $data = json_decode(base64_decode($ti[1]));
        var_dump($data); // this will contain our originalTransactionId
    }
} else {
    echo 'Header is not valid';
    exit;
}

Using firebase/php-jwt in composer (recommended), big difference is to use the public key to decode the payload using JWT.

composer require firebase/php-jwt
<?php

ini_set('display_errors', 1);
error_reporting(E_ALL);

// No need these 3 lines for Laravel
require_once './vendor/firebase/php-jwt/src/JWT.php';
require_once './vendor/firebase/php-jwt/src/JWK.php';
require_once './vendor/firebase/php-jwt/src/Key.php';

use Firebase\JWT\JWT;
use Firebase\JWT\Key;

// Download the certificate -> https://www.apple.com/certificateauthority/AppleRootCA-G3.cer
// Convert it to .PEM file, run on macOS terminal ->  ```bash openssl x509 -in AppleRootCA-G3.cer -out apple_root.pem```

$pem = file_get_contents('apple_root.pem');

$data = file_get_contents('notification.json');  // replace with file_get_contents('php://input');
$json = json_decode($data);

$header_payload_secret = explode('.', $json->signedPayload);

//------------------------------------------
// Header
//------------------------------------------
$header = json_decode(base64_decode($header_payload_secret[0]));
$algorithm = $header->alg;
$x5c = $header->x5c; // array
$certificate = $x5c[0];
$intermediate_certificate = $x5c[1];
$root_certificate = $x5c[2];

$certificate =
      "-----BEGIN CERTIFICATE-----\n"
    . $certificate
    . "\n-----END CERTIFICATE-----";

$intermediate_certificate =
      "-----BEGIN CERTIFICATE-----\n"
    . $intermediate_certificate
    . "\n-----END CERTIFICATE-----";

$root_certificate =
      "-----BEGIN CERTIFICATE-----\n"
    . $root_certificate
    . "\n-----END CERTIFICATE-----";

//------------------------------------------
// Verify the notification request   
//------------------------------------------

if (openssl_x509_verify($intermediate_certificate, $root_certificate) != 1){ 
    echo 'Intermediate and Root certificate do not match';
    exit;
}

// Verify again with Apple root certificate
if (openssl_x509_verify($root_certificate, $pem) == 1){
    $cert_object = openssl_x509_read($certificate);
    $pkey_object = openssl_pkey_get_public($cert_object);
    $pkey_array = openssl_pkey_get_details($pkey_object);
    $publicKey = $pkey_array['key'];

    //------------------------------------------
    // Payload
    //------------------------------------------
    $payload = json_decode(base64_decode($header_payload_secret[1]));
    $notificationType = $payload->notificationType;

    //if ($notificationType == "EXPIRED" || $notificationType == "REFUND") {
        $transactionInfo = $payload->data->signedTransactionInfo;
        $signedRenewalInfo = $payload->data->signedRenewalInfo;

        $transactionDecodedData = JWT::decode($transactionInfo, new Key($publicKey, $algorithm));
        var_dump($transactionDecodedData->originalTransactionId);
        echo "========================================";
        $signedRenewalDecodedData = JWT::decode($signedRenewalInfo, new Key($publicKey, $algorithm));
        var_dump($signedRenewalDecodedData);
    //}

} else {
    echo 'Header is not valid';
    exit;
}

Download the source code

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