[in_app_purchase] Return jwsRepresentation and jsonRepresentation for StoreKit2 (flutter#9280)

Fix for flutter/flutter#164433

Providing access to `jwsRepresentation`. property of the transaction. With the most recent update `PurchaseVerificationData` returns empty now. I think it could make sense to repurpose it and return the:
- `jsonRepresentation` for `localVerificationData`
-  `jwsRepresentation` for  `serverVerificationData`

## Pre-Review Checklist

[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.

Author: shaunpanjabi

packages/in_app_purchase/in_app_purchase_storekit/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 0.4.2
+
+* Add [jwsRepresentation](https://developer.apple.com/documentation/storekit/verificationresult/jwsrepresentation-21vgo) to `SK2PurchaseDetails` as `serverVerificationData` for secure server-side purchase verification. Use this JSON Web Signature (JWS) value to perform your own JWS verification on your server.
+* Add [jsonRepresentation](https://developer.apple.com/documentation/storekit/transaction/jsonrepresentation) to `SK2PurchaseDetails` as `localVerificationData` for local transaction debugging and verification.
+
 ## 0.4.1
 
 * Updates minimum supported SDK version to Flutter 3.27/Dart 3.6.

packages/in_app_purchase/in_app_purchase_storekit/darwin/in_app_purchase_storekit/Sources/in_app_purchase_storekit/StoreKit2/InAppPurchasePlugin+StoreKit2.swift

@@ -88,7 +88,8 @@ extension InAppPurchasePlugin: InAppPurchase2API {
         case .success(let verification):
           switch verification {
           case .verified(let transaction):
-            self.sendTransactionUpdate(transaction: transaction)
+            self.sendTransactionUpdate(
+              transaction: transaction, receipt: verification.jwsRepresentation)
             completion(.success(result.convertToPigeon()))
           case .unverified(_, let error):
             completion(.failure(error))
@@ -284,7 +285,8 @@ extension InAppPurchasePlugin: InAppPurchase2API {
         for await verificationResult in Transaction.updates {
           switch verificationResult {
           case .verified(let transaction):
-            self?.sendTransactionUpdate(transaction: transaction)
+            self?.sendTransactionUpdate(
+              transaction: transaction, receipt: verificationResult.jwsRepresentation)
           case .unverified:
             break
           }

packages/in_app_purchase/in_app_purchase_storekit/lib/src/store_kit_2_wrappers/sk2_transaction_wrapper.dart

@@ -121,7 +121,10 @@ extension on SK2TransactionMessage {
       // receipt isn’t necessary with SK2 as a Transaction can only be returned
       // from validated purchases.
       verificationData: PurchaseVerificationData(
-          localVerificationData: '', serverVerificationData: '', source: ''),
+          localVerificationData: jsonRepresentation ?? '',
+          // receiptData is the JWS representation of the transaction
+          serverVerificationData: receiptData ?? '',
+          source: kIAPSource),
       transactionDate: purchaseDate,
       // Note that with SK2, any transactions that *can* be returned will
       // require to be finished, and are already purchased.

packages/in_app_purchase/in_app_purchase_storekit/pubspec.yaml

@@ -2,7 +2,7 @@ name: in_app_purchase_storekit
 description: An implementation for the iOS and macOS platforms of the Flutter `in_app_purchase` plugin. This uses the StoreKit Framework.
 repository: https://github.com/flutter/packages/tree/main/packages/in_app_purchase/in_app_purchase_storekit
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+in_app_purchase%22
-version: 0.4.1
+version: 0.4.2
 
 environment:
   sdk: ^3.6.0

packages/in_app_purchase/in_app_purchase_storekit/test/fakes/fake_storekit_platform.dart

@@ -442,5 +442,7 @@ SK2TransactionMessage createPendingTransaction(String id, {int quantity = 1}) {
       originalId: 2,
       productId: id,
       purchaseDate: 'purchaseDate',
-      appAccountToken: 'appAccountToken');
+      appAccountToken: 'appAccountToken',
+      receiptData: 'receiptData',
+      jsonRepresentation: 'jsonRepresentation');
 }

packages/in_app_purchase/in_app_purchase_storekit/test/in_app_purchase_storekit_2_platform_test.dart

@@ -154,6 +154,38 @@ void main() {
           throwsA(isInstanceOf<AssertionError>()));
     });
 
+    test(
+        'buying consumable, should get PurchaseVerificationData with serverVerificationData and localVerificationData',
+        () async {
+      final List<PurchaseDetails> details = <PurchaseDetails>[];
+      final Completer<List<PurchaseDetails>> completer =
+          Completer<List<PurchaseDetails>>();
+      final Stream<List<PurchaseDetails>> stream =
+          iapStoreKitPlatform.purchaseStream;
+
+      late final StreamSubscription<List<PurchaseDetails>> subscription;
+      subscription = stream.listen((List<PurchaseDetails> purchaseDetailsList) {
+        details.addAll(purchaseDetailsList);
+        if (purchaseDetailsList.first.status == PurchaseStatus.purchased) {
+          completer.complete(details);
+          subscription.cancel();
+        }
+      });
+      final AppStorePurchaseParam purchaseParam = AppStorePurchaseParam(
+          productDetails:
+              AppStoreProduct2Details.fromSK2Product(dummyProductWrapper),
+          applicationUserName: 'appName');
+      await iapStoreKitPlatform.buyConsumable(purchaseParam: purchaseParam);
+
+      final List<PurchaseDetails> result = await completer.future;
+      expect(result.length, 1);
+      expect(result.first.productID, dummyProductWrapper.id);
+      expect(
+          result.first.verificationData.serverVerificationData, 'receiptData');
+      expect(result.first.verificationData.localVerificationData,
+          'jsonRepresentation');
+    });
+
     test('should process Sk2PurchaseParam with winBackOfferId only', () async {
       final Sk2PurchaseParam purchaseParam = Sk2PurchaseParam(
         productDetails: