Google Play Android Developer API from C#/.NET service - (400) Bad Request

Question

I'm trying to access a Purchase Status API from my ASP.NET web server using Google APIs .NET Client Library which is a recommended way for using Purchase API v1.1. However, the Authorization page of this API suggests direct web requests to Google's OAuth2 pages instead of using the corresponding client libraries.

OK, I tried both methods with all variations I could imagine and both of them lead to "The remote server returned an error: (400) Bad Request.".

Now what I've done to get to my point. First I've made all steps 1-8 under the Creating an APIs Console project of the Authorization page. Next I generated a refresh token as described there. During refresh token generation I chose the same Google account as I used to publish my Android application (which is in published beta state now).

Next I've created a console C# application for test purposes in Visual Studio (may be console app is the problem?) and tried to call the Purchase API using this code (found in some Google API examples):

    private static void Main(string[] args)
    {
        var provider =
            new WebServerClient(GoogleAuthenticationServer.Description)
                {
                    ClientIdentifier = "91....751.apps.googleusercontent.com",
                    ClientSecret = "wRT0Kf_b....ow"
                };
        var auth = new OAuth2Authenticator<WebServerClient>(
            provider, GetAuthorization);

        var service = new AndroidPublisherService(
            new BaseClientService.Initializer()
                {
                    Authenticator = auth,
                    ApplicationName = APP_NAME
                });

        var request = service.Inapppurchases.Get(
            PACKAGE_NAME, PRODUCT_ID, PURCHASE_TOKEN);
        var purchaseState = request.Execute();

        Console.WriteLine(JsonConvert.SerializeObject(purchaseState));
    }

    private static IAuthorizationState GetAuthorization(WebServerClient client)
    {
        IAuthorizationState state =
            new AuthorizationState(
                new[] {"https://www.googleapis.com/auth/androidpublisher"})
                {
                    RefreshToken = "4/lWX1B3nU0_Ya....gAI"
                };

        // below is my redirect URI which I used to get a refresh token
        // I tried with and without this statement
        state.Callback = new Uri("https://XXXXX.com/oauth2callback/");

        client.RefreshToken(state); // <-- Here we have (400) Bad request
        return state;
    }

Then I tried this code to get the access token (I found it here: Google Calendar API - Bad Request (400) Trying To Swap Code For Access Token):

    public static string GetAccessToken()
    {
        var request = WebRequest.Create(
            "https://accounts.google.com/o/oauth2/token");
        request.Method = "POST";
        var postData =
            string.Format(
                @"code={0}&client_id={1}&client_secret={2}&redirect_uri={3}&grant_type=authorization_code",
            // refresh token I got from browser
            // also tried with Url encoded value
            // 4%2FlWX1B3nU0_Yax....gAI
                "4/lWX1B3nU0_Yax....gAI",
            // ClientID from Google APIs Console
                "919....1.apps.googleusercontent.com",
            // Client secret from Google APIs Console
                "wRT0Kf_bE....w",
            // redirect URI from Google APIs Console
            // also tried Url encoded value
            // https%3A%2F%2FXXXXX.com%2Foauth2callback%2F
                "https://XXXXX.com/oauth2callback/");

        byte[] byteArray = Encoding.UTF8.GetBytes(postData);
        request.ContentType = "application/x-www-form-urlencoded";
        request.ContentLength = byteArray.Length;
        using (var dataStream = request.GetRequestStream())
        {
            dataStream.Write(byteArray, 0, byteArray.Length);
            dataStream.Close();
        }
        try
        {
            // request.GetResponse() --> (400) Bad request again!
            using (var response = request.GetResponse())
            {
                using (var dataStream = response.GetResponseStream())
                {
                    using (var reader = new StreamReader(dataStream))
                    {
                        var responseFromServer = reader.ReadToEnd();
                        var jsonResponse = JsonConvert.DeserializeObject<OAuth2Response>(responseFromServer);
                        return jsonResponse.access_token;
                    }
                }
            }
        }
        catch (Exception ex) { var x = ex; }
        return null;
    }

So, to sum up all my long story:

1. Is it possible at all to pass OAuth2 authorization using either of methods above from a C# Console Application (without user interaction)?
2. I've double checked the redirect URI (since I saw a lot of discussed troubles because of it here on stackoverflow) and other parameters like ClientID and ClientSecret. What else I could do wrong in the code above?
3. Do I need to URL encode a slash in the refresh token (I saw that the first method using client library does it)?
4. What is the recommended way of achieving my final goal (Purchase API access from ASP.NET web server)?

Answer 1

I'll try to answer your last question. If you access your own data account, you dont need to use client id in oAuth2. Let's use service account to access Google Play API.

1. Create a service account in Google Developer Console > Your project > APIs and auth > Credentials > Create a new key. You will download a p12 key.
2. Create a C# project. You can choose console application.
3. Install google play api library from Google.Apis.androidpublisher. Nuget. You can find other library for dotnet in Google APIs Client Library for .NET

4. Link google api project with your google play account in API access

5. Authenticate and try to query information. I'll try with listing all inapp item. You can just change to get purchase's status

   String serviceAccountEmail = "[email protected]";
   
       var certificate = new X509Certificate2(@"physical-path-to-your-key\key.p12", "notasecret", X509KeyStorageFlags.Exportable);
   
       ServiceAccountCredential credential = new ServiceAccountCredential(
          new ServiceAccountCredential.Initializer(serviceAccountEmail)
          {
              Scopes = new[] { "https://www.googleapis.com/auth/androidpublisher" }
          }.FromCertificate(certificate));
   
   
       var service = new AndroidPublisherService(
      new BaseClientService.Initializer()
      {
          HttpClientInitializer = credential,
          ApplicationName = "GooglePlay API Sample",
      });
   // try catch this function because if you input wrong params ( wrong token) google will return error.
       var request = service.Inappproducts.List("your-package-name");
       var purchaseState = request.Execute();
   
      // var request = service.Purchases.Products.Get(
      //"your-package-name", "your-inapp-item-id", "purchase-token"); get purchase'status
   
   
   
       Console.WriteLine(JsonConvert.SerializeObject(purchaseState));