Android in-app billing Verification of Receipt in Dot Net(C#)

Android In-App Billing Receipt Verification in Dot Net (C#)

In-app purchases are a popular way for Android developers to monetize their apps. To ensure the security and validity of these purchases, Google provides a mechanism for verifying purchase receipts.

This article will guide you through the process of verifying Android in-app billing receipts in a Dot Net (C#) application.

Understanding the Process

The receipt verification process involves the following steps:

• Retrieve the purchase receipt from your Android app.
• Send the receipt to your server for verification.
• Use Google’s API to validate the receipt.
• Process the verification result.

Setting Up Your Server-Side Environment

1. Prerequisites

• .NET Framework or .NET Core: Choose the version compatible with your project.
• Google Cloud Platform Project: You’ll need a Google Cloud Platform project to use the Google API.
• API Key: Create an API key for your Google Cloud project and restrict its usage to the Google Play Billing API.

2. Install Required Libraries

You’ll need to install the necessary libraries to communicate with Google’s API. In your project, install the Google.Apis.AndroidPublisher.v3 NuGet package.

3. Configure the API Client

Create a class to handle the communication with the Google Play Billing API:

using Google.Apis.AndroidPublisher.v3;
using Google.Apis.AndroidPublisher.v3.Data;
using Google.Apis.Auth.OAuth2;
using Google.Apis.Services;

public class BillingClient
{
    private readonly AndroidPublisherService _service;

    public BillingClient(string apiKey)
    {
        var credential = new ServiceAccountCredential(
            new ServiceAccountCredential.Initializer(apiKey)
                .Scopes(AndroidPublisherService.Scope.Androidpublisher)
        );
        _service = new AndroidPublisherService(new BaseClientService.Initializer()
        {
            HttpClientInitializer = credential,
            ApplicationName = "Your Application Name"
        });
    }

    public async Task VerifyPurchaseAsync(string packageName, string purchaseToken)
    {
        var request = _service.Purchases.Get(packageName, purchaseToken);
        var response = await request.ExecuteAsync();
        return response != null;
    }
}

4. Handle Receipt Verification

Create a method to receive the purchase receipt from your Android app, verify it with Google’s API, and process the result.

using System.Net.Http;
using System.Text.Json;

public class ReceiptVerificationService
{
    private readonly HttpClient _httpClient;
    private readonly BillingClient _billingClient;

    public ReceiptVerificationService(HttpClient httpClient, BillingClient billingClient)
    {
        _httpClient = httpClient;
        _billingClient = billingClient;
    }

    public async Task VerifyReceipt(string purchaseToken)
    {
        // Your app ID on Google Play
        var packageName = "com.your.package.name";

        // Verify the purchase token using the Google Play Billing API
        var isVerified = await _billingClient.VerifyPurchaseAsync(packageName, purchaseToken);

        // Handle the verification result
        if (isVerified)
        {
            // Purchase is valid
            Console.WriteLine("Purchase is valid.");
            // Process the purchase (e.g., unlock premium features)
        }
        else
        {
            // Purchase is invalid
            Console.WriteLine("Purchase is invalid.");
            // Handle invalid purchase (e.g., display an error message)
        }

        return isVerified;
    }
}

Integrating with Your Android App

1. Send the Receipt

In your Android app, use the Purchases.getPurchaseHistory method to retrieve the purchase receipt data (including the purchase token).

Send this data to your server using an HTTP request (e.g., POST method). Make sure to securely transmit the receipt to your server.

2. Handle Response

After your server verifies the purchase, send back a response to your Android app. This response should indicate the verification result (success or failure). Based on the response, you can:

• Grant access to purchased content.
• Display appropriate messages to the user.
• Take necessary actions based on the purchase status.

Security Considerations

• Protect Your API Key: Never hardcode your API key in your client code. Keep it secure on your server and access it only through authorized channels.
• Use Secure Communication: Implement HTTPS to secure the communication between your Android app and your server.
• Validate Inputs: Always validate the purchase token and other data received from your Android app to prevent vulnerabilities.

Conclusion

By following these steps, you can effectively verify Android in-app billing receipts in your Dot Net (C#) applications, ensuring secure and reliable purchase transactions for your app users.