Spring Boot authentication with GCP OpenID

Application.java

package com.rich.gcp.app;

import com.google.api.client.http.GenericUrl;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.gax.core.CredentialsProvider;
import com.google.auth.http.HttpCredentialsAdapter;
import com.google.auth.oauth2.GoogleCredentials;
import com.google.auth.oauth2.IdTokenCredentials;
import com.google.auth.oauth2.IdTokenProvider;
import com.google.cloud.spring.core.GcpProjectIdProvider;
import com.google.common.base.Charsets;
import com.google.common.io.CharStreams;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

import java.io.IOException;
import java.io.InputStreamReader;

@SpringBootApplication
public class Application implements CommandLineRunner {

	private static String SERVICE_URL = "https://hello-spring-auth-yrufibgptq-de.a.run.app";

	@Autowired
	GcpProjectIdProvider gcpProjectIdProvider;

	@Autowired
	CredentialsProvider credentialsProvider;

	public static void main(String[] args) {
		SpringApplication.run(Application.class, args);
	}

	@Override
	public void run(String... args) throws Exception {
		System.out.println(gcpProjectIdProvider.getProjectId());
		GoogleCredentials credentials = (GoogleCredentials) credentialsProvider.getCredentials();
		if (!(credentials instanceof IdTokenProvider)) {
			throw new IllegalArgumentException("Credentials are not an instance of IdTokenProvider.");
		}

		IdTokenCredentials tokenCredential =
				IdTokenCredentials.newBuilder()
						.setIdTokenProvider((IdTokenProvider) credentials)
						.setTargetAudience(SERVICE_URL)
						.build();

		invokeService(tokenCredential);
	}

	private void invokeService(IdTokenCredentials tokenCredential) throws IOException {
		GenericUrl genericUrl = new GenericUrl(SERVICE_URL);
		HttpCredentialsAdapter adapter = new HttpCredentialsAdapter(tokenCredential);
		HttpTransport transport = new NetHttpTransport();
		HttpRequest request = transport.createRequestFactory(adapter).buildGetRequest(genericUrl);
		HttpResponse response = request.execute();

		int statusCode = response.getStatusCode();
		if (statusCode != 200) {
			throw new IOException(
					"Bad status code: " + statusCode + " error: " + response.getStatusMessage());
		}

		String body = CharStreams
				.toString(new InputStreamReader(response.getContent(), Charsets.UTF_8));
		System.out.println(body);
	}

}