Get started using App Check with a custom provider with C++

This page shows you how to enable App Check in a C++ app, using your custom App Check provider. When you enable App Check, you help ensure that only your app can access your project's Firebase resources.

If you want to use App Check with the default providers, see Enable App Check with default providers with C++.

Before you begin

1. Add the App Check library to your app

Include the App Check library in your set of dependencies, following the setup instructions for App Check.

2. Implement the App Check interfaces

First, you need to create classes that implement the AppCheckProvider and AppCheckProviderFactory interfaces.

Your AppCheckProvider class must have a GetToken() method, which collects whatever information your custom App Check provider requires as proof of authenticity, and sends it to your token acquisition service in exchange for an App Check token. The App Check SDK handles token caching, so always get a new token in your implementation of GetToken().

class YourCustomAppCheckProvider : public AppCheckProvider {
  void GetToken(std::function<void(AppCheckToken, int, const std::string&)>
      completion_callback) {
    // Logic to exchange proof of authenticity for an App Check token and
    //   expiration time.
    // ...

    // Create AppCheckToken object.
    AppCheckToken appCheckToken;
    appCheckToken.token = token;
    appCheckToken.expire_time_millis = expireTime;

    completion_callback(appCheckToken, 0, "");

    // Or, if needing to return an error
    //completion_callback({}, error_code, "Error description");
  }
};

Also, implement a AppCheckProviderFactory class that creates instances of your AppCheckProvider implementation:

class YourCustomAppCheckProviderFactory : public AppCheckProviderFactory {
  AppCheckProvider* CreateProvider(App* app) {
    // Create and return an AppCheckProvider object.
    return new YourCustomAppCheckProvider(app);
  }
}

3. Initialize App Check

Add the following initialization code to your app so that it runs before you use any other Firebase SDKs:

firebase::app_check::AppCheck::SetAppCheckProviderFactory(
    YourCustomAppCheckProviderFactory::GetInstance());

Next steps

Once the App Check library is installed in your app, start distributing the updated app to your users.

The updated client app will begin sending App Check tokens along with every request it makes to Firebase, but Firebase products will not require the tokens to be valid until you enable enforcement in the App Check section of the Firebase console.

Monitor metrics and enable enforcement

Before you enable enforcement, however, you should make sure that doing so won't disrupt your existing legitimate users. On the other hand, if you're seeing suspicious use of your app resources, you might want to enable enforcement sooner.

To help make this decision, you can look at App Check metrics for the services you use:

Enable App Check enforcement

When you understand how App Check will affect your users and you're ready to proceed, you can enable App Check enforcement:

Use App Check in debug environments

If, after you have registered your app for App Check, you want to run your app in an environment that App Check would normally not classify as valid, such as an emulator during development, or from a continuous integration (CI) environment, you can create a debug build of your app that uses the App Check debug provider instead of a real attestation provider.

See Use App Check with the debug provider with C++.