Develop Reference

The 'destination' param cannot be set to your own account. Stripe

I create a manage account . And I create another test account for send payment to it. I want to get payment with managed account get application fee for it. and I will send the remaining of the payment to test account .
Stripe.apiKey = "sk_test_...";
Map<String, Object> chargeParams = new HashMap<String, Object>();
chargeParams.put("amount", 1000);
chargeParams.put("currency", "usd");
chargeParams.put("source", {TOKEN});
chargeParams.put("destination", {CONNECTED_STRIPE_ACCOUNT_ID});
Charge.create(chargeParams);
But I get this exception "The 'destination' param cannot be set to your own account". I dont know where I make mistake.

You should not be creating charges directly from your Android app.
The only part of the payment flow that takes place directly in a mobile app is the collection and tokenization of the customer's payment information, through the use of Stripe's Android SDK. This is done with your publishable API key.
All other operations require the use of your secret API key, which should never be embedded or shared in any way with your mobile app, as it would then be easy for an attacker to retrieve it and use it to access your account.
Once you've collected the customer's payment information and created a token, you need to send this token to a backend server where you can use it to create a charge or a customer.
In regard to the specific error you're seeing, it's happening because you set the destination parameter to your own account's ID. When creating charges through the platform, the destination parameter must be set to the ID of an account that is connected to your platform, not your own platform's account ID.

Call an API on AWS API Gateway using Cognito Credentials from Android

I am trying to use AWS API Gateway generated android SDK to call an API using amazon Cognito for authentication made using AWS API Gateway. Cant understand how to call the api's. Any pointers on how to make an API call from android using the generated API Gateway Android SDK. Have went through a lot of articles.

It might seem a bit confusing to start with. But it is similar to a normal SDK we use.
Let's say you have a user post in your API, and you want to create a user with few parameters like name, email, phone number according to the json your API's accept, your code will look something like
You create an instance of your SDK with:
credentialsProvider = new CognitoCachingCredentialsProvider(
context,
"identityPoolID",
AMAZON_COGNITO_REGION
);
factory = new ApiClientFactory().credentialsProvider(credentialsProvider)
.endpoint("<endpoint>");
INSTANCE.client = INSTANCE.factory.build(<class>.class);
You create an object of the User with:
UserModel output = new UserModel();
output.setFirstName("something");
output.setEmail("abc#xyc.com");
And then you make a user post with:
client.usersPost(output);
Hope it's clear.

How do I restrict Google App Engine Endpoints API access to only my Android applications?

I am an Android developer building my first Google App Engine (java) back-end for my apps. I don't want anybody else to access this API other than my app. (I plan to use App engine for verifying InApp purchases in my Android app). My data is not relevant to users so,
I don't want users to be able to access my API even if they are logged in with their Google accounts (on web or Android devices).
I followed the steps mentioned in - "Specifying authorized clients in the API backend"
(https://developers.google.com/appengine/docs/java/endpoints/auth)
like generating client IDs and add them in #Api (clientIds and audiences)
except "Add a User parameter" - since I don't need user authentication.
Then I deployed App engine and I am still able to access the API through API explorer (https://your_app_id.appspot.com/_ah/api/explorer)
(I haven't added API_EXPLORER client ID)
I tested with the APK that was built with the endpoint libs before adding client IDs and can still access the API.
Is adding a "User parameter" to all endpoint APIs a must? to achieve my purpose (restrict API to only my Android apps).
Can I pass null as userAccount name from Android client and ignore user parameter value on server (since it will be null)? Will this ensure that the API is accessible only from my android apps (since the client ID is generated for my package name and SHA1 of the APK?)
Should I use something like a service account for this purpose?
The documentation says for Android, both Android and Web client IDs must be added and audience must be the same as web client ID. Does this open access to any other web client? can I skip mentioning web client ID and still achieve my purpose?
Appreciate your time and help.
...... updating with my further investigation ...
I did the following:
Added User parameter to APIs on backend - but did not check for null value. API can still be accessed without passing any credentials (from Android debug APK and API explorer)
Then, I tried
mCredential = GoogleAccountCredential.usingAudience(this, "server:client_id:" + WEB_CLIENT_ID);
mCredential.setSelectedAccountName(null);
and passed this credential to API builder (as suggested in some other posts)
Caused FATAL EXCEPTION. So, we can't pass null account name.
I could call the API using API explorer without OAuth. But when I enabled OAuth, it gave error saying this client ID is not allowed! ( I haven't yet added com.google.api.server.spi.Constant.API_EXPLORER_CLIENT_ID in client_ids{})
Then I added code to throw OAuthRequestException on the backend if the user is null. This resulted in API explorer getting errors without OAuth. It works with OAuth enabled after adding API_EXPLORER_CLIENT_ID to client_ids)
Added code to pass valid user account name(email) from my Android app. Then, I am able to access API only with my release APK. Even the debug APK gets exceptions! - which is what I expected..So, I assume no other Android apps will be able to access this API.
So, not checking for null user on back-end API is a bad idea (as suggested in other posts). It is as good as not mentioning any client_ids and not having User param.
Only question I have at this moment is: If some one can figure out the WEB_CLIENT_ID from the APK, will they be able to use it to build a web client to access my API (I haven't mentioned client secret anywhere in the code. So I am thinking this is not possible).
I did search Google groups and Stackoverflow, but still it is not clear.
(Authenticate my “app” to Google cloud endpoints not a “user”)
Authenticate my "app" to Google Cloud Endpoints not a "user"
(How do I protect my API that was built using Google Cloud Endpoints?)
How do I protect my API that was built using Google Cloud Endpoints?
(Restrict access to google cloud endpoints to Android app)
Restrict access to google cloud endpoints to Android app

I had a similar issue, not between Android and App Engine, but between a separate server and App Engine. The way I handled it was to add a signature hash field as a parameter to each API call. If the request had an improper signature, it would be denied.
For example, suppose your API end-point is example.com/api/do_thing?param1=foo. I would hash the entire url, along with a secret key, and then append the result of the hash to the request: example.com/api/do_thing?param1=foo&hash=[some long hex value].
Then, on the server side, I would first remove the hash from the url request, then run the hash on everything that was remaining. Finally, you check whether the calculated hash matches the one that was sent with the request and if they don't, you can deny the request.
It is very important however that your secret key remain secret. You have to be careful with this on Android because someone could attempt to decompile your APK.

Facing the same problem than you ! Authenticate Android End point without Google User Account is just impossible !
So here is my way to resolv this problem, without any user interaction (Maybe not the right but that works, and you've got strong authentication (SHA1 + Google Account)):
HERE IS MY ANDROID CODE
Get and Build Valid Credential
//Get all accounts from my Android Phone
String validGoogleAccount = null;
Pattern emailPattern = Patterns.EMAIL_ADDRESS; // API level 8+
Account[] accounts = AccountManager.get(context).getAccounts();
for (Account account : accounts) {
if (emailPattern.matcher(account.name).matches()) {
//Just store mail if countain gmail.com
if (account.name.toString().contains("gmail.com")&&account.type.toString().contains("com.google")){
validGoogleAccount=account.name.toString();
}
}
}
//Build Credential with valid google account
GoogleAccountCredential credential = GoogleAccountCredential.usingAudience(this,"server:client_id:301991144702-5qkqclsogd0b4fnkhrja7hppshrvp4kh.apps.googleusercontent.com");
credential.setSelectedAccountName(validGoogleAccount);
Use this credential for secure calls
Campagneendpoint.Builder endpointBuilder = new Campagneendpoint.Builder(AndroidHttp.newCompatibleTransport(), new JacksonFactory(), credential);
HERE IS MY API BACKEND CODE:
API Annotation
#Api(
scopes=CONSTANTES.EMAIL_SCOPE,
clientIds = {CONSTANTES.ANDROID_CLIENT_ID,
CONSTANTES.WEB_CLIENT_ID,
com.google.api.server.spi.Constant.API_EXPLORER_CLIENT_ID},
audiences = {CONSTANTES.ANDROID_AUDIENCE},
name = "campagneendpoint",
version = "v1"
)
Method code:
public Collection<Campagne> getCampagnes(#Named("NumPortable")String NumPortable, User user) throws UnauthorizedException {
if (user == null) throw new UnauthorizedException("User is Not Valid");
return CampagneCRUD.getInstance().findCampagne(NumPortable);
}
For the moment, it only works on Android (I don't know how we gonna do on IOS..)..
Hope It will help you !

Google provides ways to do this for Android, web and iOS
The steps involves:
Specifying a client Id for apps you want to allow to make requests to your API
Adding a User parameter to all exposed methods to be protected by authorization.
Generating the client library again for any Android clients
Redeploying your backend API.
Updating the regenerated jar file to your Android project for your Android client.
These steps are laid out in clear detail on Google's Using Auth with Endpoints and also on this blog

Facing the same problem, here are the result of my research :
Added Android cliend id with SHA1 fingerprint in Google console
Use of it in the API annotation
BUT :
If i dont add user parameter to methods : the check about android app client id does not work
If I add the USER parameter but do not ask the user to choose its google account to create the credential ... also it does not work ...
Conclusion : It seems to be mandatory to connect a user account for the check about the app client id to be executed ... I really do not understand why because no link exist between the 2 processes

Access this site
Choose your project, go to credentials section
Create a new api key
Create a new android key
Click on "Edit allowed android applications" and enter your SHA1 key; your android package name
Let me know if this solves the issues.

Error 401 Google-api-php-client verifing by server Android inapppurchase

I need to verify on my server each Android purchase that was made before by user in my Android APP.
I though that working with google-api-php-client it would be easy the authentication and managing of the token in server. But there aren't any sample, and yesterday Google published new version 0.6.3 providing in-app-purchases service.
I followed -> *code.google.com/p/google-api-php-client/wiki/OAuth2#Service_Accounts*
On my code.google.com/apis/console/ I pushed on, "Google Play Android Developer API" and I configured the "service account" in API Access.
From Android client APP, server recives the PACKAGE_NAME, PRODUCT_ID and purchase TOKEN.
My server code is the following:
require_once '../../src/Google_Client.php';
require_once '../../src/contrib/Google_AndroidpublisherService.php';
// Set your client id, service account name, and the path to your private key.
// For more information about obtaining these keys, visit:
// https://developers.google.com/console/help/#service_accounts
const CLIENT_ID = 'asdf.apps.googleusercontent.com';
const SERVICE_ACCOUNT_NAME = 'asdf#developer.gserviceaccount.com';
// Make sure you keep your key.p12 file in a secure location, and isn't
// readable by others.
const KEY_FILE = '../../asdf/privatekey.p12';;
$client = new Google_Client();
$client->setApplicationName({APP_PACKAGE_NAME});
// Set your cached access token. Remember to replace $_SESSION with a
// real database or memcached.
session_start();
if (isset($_SESSION['token'])) {
$client->setAccessToken($_SESSION['token']);
}
// Load the key in PKCS 12 format (you need to download this from the
// Google API Console when the service account was created.
$key = file_get_contents(KEY_FILE);
$client->setAssertionCredentials(new Google_AssertionCredentials(
SERVICE_ACCOUNT_NAME,
array('https://www.googleapis.com/auth/androidpublisher'),
$key)
);
$client->setClientId(CLIENT_ID);
$service = new Google_AndroidPublisherService($client);
$res = $service->inapppurchases->get({APP_PACKAGE_NAME},{APP_PACKAGE_NAME.PRODUCT_ID}, {PURCHASE_TOKEN});
var_dump($res);
The error showed is:
Google_ServiceException: Error calling GET https://www.googleapis.com/androidpublisher
/v1.1/applications/{APP_PACKAGE_NAME}/inapp/{APP_PACKAGE_NAME.PRODUCT_ID}/purchases
/{PURCHASE_TOKEN}: (401) This developer account does not own the application. in
/.../google-api-php-client/src/io/Google_REST.php on line 66 Call Stack: 0.0201
266376 1. {main}() ............
Token is correct, and I'm working with the same account in Google API Console(https://code.google.com/apis/console) and Google Developer Console (https://play.google.com/apps/publish/). I'm only using Service account api, and don't working with Client ID for web applications, and Simple API Access. For security I changed here some code values.
Could somebody help me to know what's wrong on my purchase server verification using Google API please?How I know the owner of my app? Have something to do with Google Apis new project, project domain, project number, project ID, etc...?

I think my problem was because I was trying to use Service Accounts with a Google Apps Gmail own account ( non #gmail.com account ).
I had to delegate domain-wide authority to my service account.
And I had to instantiate a Android Publisher Service as follows: ( only founded in Google Api Drive documentation ).
I added "sub" parameter programmatically in Google_AssertionCredentials like follows:
$auth = new Google_AssertionCredentials(
SERVICE_ACCOUNT_NAME,
'https://www.googleapis.com/auth/androidpublisher',
$key);
$auth->sub = "myown#email.com";
$client->setAssertionCredentials($auth);
The documentation in Google Play Android Developer API is very poor, and Google Support doesn't help, they redirects you to documentation. Google PHP developers even don't know how Service Accounts works.
In spite of having found the answer by myself, Google needs to improve all new Google Play In-app Billing API version 3.

Am I getting the steps right for verifying a user's Android in-app subscription?

I am making an app that does not require a user account/login, and allows the user to purchase a subscription. I want to use the Google Play Developer API to verify whether or not a user has a purchased/active subscription. From all of the documentation, I've gathered the following steps.
Are they correct, and could you answer the two questions in them?
Create a Service Account in the Google APIs Console.
Save the private key that is given to me (where? surely not in my code/on the device as this sample code suggests)
Use Google APIs Client Library for Java to create and sign a JWT with the private key (how? the docs give me this, but that is not Java code... What do I do with it?)
Construct an access token request, and get access to the API
Application can now send a GET request to the API to find out whether or not the
user has a subscription
When the access token expires, go back to step 3.
Also, I have a web service, though I know nothing about web services or web service programming... I only know enough to be aware that it is probably necessary to use here.
EDIT: These steps were not correct. See my answer below for the correct steps. However, note that this only applies to using a service account (because I did not want to require a user to have to explicitly allow API access)

As it turns out, my steps were not correct. It took me weeks to figure this out and it doesn't seem to be documented anywhere else. You're welcome:
Create a Web Application account in the Google APIs Console. Put any website as a "redirect URI"; it doesn't matter since you will not really be using it. You will get a client id and client secret when you create the account.
In a browser on your computer go to https://accounts.google.com/o/oauth2/auth?scope=https://www.googleapis.com/auth/androidpublisher&response_type=code&access_type=offline&redirect_uri=[YOUR REDIRECT URI]&client_id=[YOUR CLIENT ID] and allow access when prompted.
Look in the address bar. At the end of the URI you entered originally will be your refresh token. It looks like 1/.... You will need this "code" in the next step. The refresh token never expires.
Convert this "code" to a "refresh token" by going to https://accounts.google.com/o/oauth2/token?client_id=[YOUR CLIENT ID]&client_secret=[YOUR CLIENT SECRET]&code=[CODE FROM PREVIOUS STEP]&grant_type=authorization_code&redirect_uri=[YOUR REDIRECT URI]. You can save the resulting value right in your program; it never expires unless explicitly revoked. (this step inserted by #BrianWhite -- see comments)
Make sure you are using POST.(inserted by Gintas)
In your code, send an HttpPost request to https://accounts.google.com/o/oauth2/token with the BasicNameValuePairs "grant_type","refresh_token", "client_id",[YOUR CLIENT ID], "client_secret",[YOUR CLIENT SECRET], "refresh_token",[YOUR REFRESH TOKEN]. For an example look here. You will need to do this in a separate thread, probably using AsyncTask. This will return a JSONObject.
Get the access token from the returned JSONObject. For an example look here. You will need to get the string "access_token". The access token expires in 1 hour.
In your code, send an HttpGet request to https://www.googleapis.com/androidpublisher/v1/applications/[YOUR APP'S PACKAGE NAME]/subscriptions/[THE ID OF YOUR PUBLISHED SUBSCRIPTION FROM YOUR ANDROID DEVELOPER CONSOLE]/purchases/[THE PURCHASE TOKEN THE USER RECEIVES UPON PURCHASING THE SUBSCRIPTION]?accesstoken="[THE ACCESS TOKEN FROM STEP 4]". For an example look here.

.NET Users: I hope this answer saves someone a ton of grief.
As #Christophe Fondacci noted on 2015, the accepted solution worked great a few years ago.
Now it's 2017 2020 and the process is far easier and faster.
My use case is to validate in-app subscriptions, where my mobile app sends subscription purchase information to my RESTful server, which in turn contacts Google to validate a subscription purchase.
The strategy is to create a Service Account that will operate on your behalf.
Sign into your Google Play Dev Console and click the app you're setting up.
Visit Settings->API access
Under Service Accounts, hit the Create Service Account button.
As of Jan 2017 a dialog with directions on setting up a service account appears. The dialog takes you to the Google API Console; from there,
A) Click Create Service Account
B) Create the service account name that makes sense. Since we're interested in accessing Android Publisher Services, I chose "publisher".
C) For Role, just choose something - you can change this later.
D) Choose "Furnish New private key" and choose P12 for .Net implementations. Don't lose this file!
Now you're done with #4, you'll see your new Service Account listed; click "Grant Access" to enable it.
Tap on the link to "View permissions". You should modify permissions based on your needs and API.
To validate in-app purchases, visit the Cog->Change Permissions and enable the GLOBAL "Visibility" and "Manage Orders" permissions.
OK at this point you have configured everything on Google's end. Now to setup your server to server stuff. I recommend creating
a .Net Console App to test out your implementation then offload it where needed.
Add the Android Publisher Client Library from Nuget[1]
PM> Install-Package Google.Apis.AndroidPublisher.v3
Add the P12 file to your project root
Change the P12 Properties so "Build Action" is "Content" and "Copy To Output Directory" to "Copy if newer".
Implement something like this to test your access and fine tune [1] .
using System.Threading.Tasks;
using System.Security.Cryptography.X509Certificates;
using Google.Apis.Services;
using Google.Apis.Auth.OAuth2;
using Google.Apis.AndroidPublisher.v3;
...
public Task<SubscriptionPurchase> GetSubscriptionPurchase(string packageName, string productId, string purchaseToken)
{
var certificate = new X509Certificate2(
"{{your p12 file name}}",
"{{ your p12 secret }}",
X509KeyStorageFlags.Exportable
);
var credentials = new ServiceAccountCredential(
new ServiceAccountCredential.Initializer("{{ your service account email }}")
{
Scopes = new[] { AndroidPublisherService.Scope.Androidpublisher }
}.FromCertificate(certificate));
var service = new AndroidPublisherService(new BaseClientService.Initializer()
{
HttpClientInitializer = credentials,
ApplicationName = "my server app name",
});
return service.Purchases.Subscriptions.Get(packageName, productId, purchaseToken).ExecuteAsync();
}
Good luck, hope this helps someone.
Sources:
Using OAuth 2.0 for Server to Server Applications
.Net Client Library for Google.Apis.AndroidPublisher.v3[1]
1 Updated 04/11/2020 - Google.Apis.AndroidPublisher.v2 EOL'd, use Google.Apis.AndroidPublisher.v3.

If you are like me, and want to do this in PHP, here is the procedure how to do it... Thanks to Kalina's answer it took me only three days to work out how it works :).
Here goes:
go to google developers console https://console.developers.google.com/ and create a web app. Put 'developers.google.com/oauthplayground'as a "redirect URI"; You will use it in step 2. You will get a client id and client secret when you create the account. Make sure you have the Google Play Android Developer API added.
go to the Google oauth2 playground https://developers.google.com/oauthplayground/. This great tool is your best friend for the next few days.
Now go to settings : make sure Use your own OAuth credentials is set. Only then you can fill in your client ID and client secret in the form below.
In Google oauth2 playground go to step 1 Select & authorize APIs fill in the scope in the input field https://www.googleapis.com/auth/androidpublisher. I couldnt find the Google Play Android Developer API in the list, maybe they will add some time later. Hit AUTORIZE APIS. Do the authorisation thing that follows.
In Google oauth2 playground go to step 2 Exchange authorization code for tokens. If all went well you will see a authorization code starting with /4. If something didnt go well check the error message on the right. Now you hit 'refresh access token'. Copy the Refresh token... it will start with /1...
Now you can always get an access token! here is how:
$url ="https://accounts.google.com/o/oauth2/token";
$fields = array(
"client_id"=>"{your client id}",
"client_secret"=>"{your client secret}",
"refresh_token"=>"{your refresh token 1/.....}",
"grant_type"=>"refresh_token"
);
$ch = curl_init($url);
//set the url, number of POST vars, POST data
curl_setopt($ch, CURLOPT_POST,count($fields));
curl_setopt($ch, CURLOPT_POSTFIELDS, $fields);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
//execute post
$lResponse_json = curl_exec($ch);
//close connection
curl_close($ch);
Now you have an ACCESS TOKEN hooray... the JSON will look like this:
"access_token" : "{the access token}", "token_type" : "Bearer", "expires_in" : 3600
Finally you're ready to ask google something! Here is how to do it:
$lAccessToken = "{The access token you got in}" ;
$lPackageNameStr = "{your apps package name com.something.something}";
$lURLStr = "https://www.googleapis.com/androidpublisher/v1.1/applications/$lPackageNameStr/subscriptions/$pProductIdStr/purchases/$pReceiptStr";
$curl = curl_init($lURLStr);
curl_setopt($curl, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
$curlheader[0] = "Authorization: Bearer " . $lAccessToken;
curl_setopt($curl, CURLOPT_HTTPHEADER, $curlheader);
$json_response = curl_exec($curl);
curl_close($curl);
$responseObj = json_decode($json_response,true);
The JSON returned will contain two timestamps, the initiationTimestampMsec and validUntilTimestampMsec the time the subscription is valid. Both are the nr of millisecs to add to the date 1/1/1970!

I don't know in 2012, but in 2015 you should not do any of these steps manually. I had a very hard time to find the documentation so I am posting here in case it helps anyone.
You should only query in-app purchases from your server for security reasons as otherwise you can trust none of the 2 ends of the purchase process.
Now on the server side (I think you could still use the same code from your app if you absolutely need to), include the google-api-services-androidpublisher client library to your project (see https://developers.google.com/api-client-library/java/apis/androidpublisher/v1)
As you mentioned, you need a service account with a P12 file (the client library only accept P12 file).
Then the following code will authenticate and get purchase information nicely:
HttpTransport httpTransport = GoogleNetHttpTransport.newTrustedTransport();
JsonFactory jsonFactory = new JacksonFactory();
List<String> scopes = new ArrayList<String>();
scopes.add(AndroidPublisherScopes.ANDROIDPUBLISHER);
Credential credential = new GoogleCredential.Builder().setTransport(httpTransport).setJsonFactory(jsonFactory)
.setServiceAccountId(googleServiceAccountId)
.setServiceAccountPrivateKeyFromP12File(new File(googleServicePrivateKeyPath))
.setServiceAccountScopes(scopes).build();
AndroidPublisher publisher = new AndroidPublisher.Builder(httpTransport, jsonFactory, credential).build();
AndroidPublisher.Purchases purchases = publisher.purchases();
final Get request = purchases.get(packageName, productId, token);
final SubscriptionPurchase purchase = request.execute();
// Do whatever you want with the purchase bean
Information on Java client authentication can be found here:
https://developers.google.com/identity/protocols/OAuth2ServiceAccount

I may misunderstand your question, but I don't see a reason for you to be using the links you're referencing to get In-App Billing for an Android app working. This page is much more helpful:
http://developer.android.com/guide/google/play/billing/index.html
You can try out the demo application they include (Dungeons -- http://developer.android.com/guide/google/play/billing/billing_integrate.html#billing-download). That uses products (one-time purchases) rather than subscriptions, but you should be able to modify to test for what you want.
I think the key, for you, would be the restoreTransactions method they provide in the sample to see if the Google Play account has any subscriptions for your app:
#Override
public void onRestoreTransactionsResponse(RestoreTransactions request, int responseCode) {
if (responseCode == BillingVars.OK) {
// Update the shared preferences so that we don't perform a RestoreTransactions again.
// This is also where you could save any existing subscriptions/purchases the user may have.
SharedPreferences prefs = getSharedPreferences(my_prefs_file, Context.MODE_PRIVATE);
SharedPreferences.Editor edit = prefs.edit();
edit.putBoolean(DB_INITIALIZED, true);
edit.commit();
} else {
Log.e(TAG, "RestoreTransactions error: " + responseCode);
}
}

If anyone is having issues with the accepted posts final step (#7), i found ?access_token= to work instead of ?accessToken=
Too bad stack overflow won't let me make that comment directly to the thread...

As you have a web service which your app can call, I would recommend storing your private key securely on your server. You should look to moving as much of the in-app stuff to service calls, as possible, see this link. I've implemented in-app subscription, but it was before this part of the API was out. I had to do my own registration and security verification but it looks like this API does most of that for you, using OAuth, although it looks like you are still responsible for storing the subscription request/verification.
Where it talks about signing your JWT's with an existing library, they do appear to provide you with links to a java library, a Python library and a PHP library - it depends what your web service or server component is written in (mine is C#, so I'm using RSACryptoServiceProvider) to verify signed purchases. They're using JSON objects for the actual transfer of data.