@Override
  public void initialize(ExtensionContext context) {
    Preconditions.checkArgument(
        !initialized, "Attempting to initialize GoogleCloudExtension more than once");
    HttpTransport httpTransport = context.getService(HttpTransport.class);
    JsonFactory jsonFactory = context.getService(JsonFactory.class);
    ObjectMapper objectMapper = context.getTypeManager().getMapper();
    String cloud = context.cloud();
    Constants.Environment environment = context.environment();
    Monitor monitor = context.getMonitor();
    GoogleCloudExtensionModule module =
        new GoogleCloudExtensionModule(
            httpTransport, jsonFactory, objectMapper, cloud, environment, monitor);
    injector = Guice.createInjector(module);
    initialized = true;
  }
{@link CloudExtension} for Google Cloud Platform.
extensions/cloud/portability-cloud-google/src/main/java/org/datatransferproject/cloud/google/GoogleCloudExtension.java