Google OAuth Playground

GoogleOAuthPlayground.java

import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.extensions.java6.auth.oauth2.AuthorizationCodeInstalledApp;
import com.google.api.client.extensions.jetty.auth.oauth2.LocalServerReceiver;
import com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeFlow;
import com.google.api.client.googleapis.auth.oauth2.GoogleClientSecrets;
import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.gson.GsonFactory;
import com.google.api.services.gmail.GmailScopes;

import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.security.GeneralSecurityException;
import java.util.Collections;
import java.util.List;

// See also: https://developers.google.com/oauthplayground/
public class GoogleOAuthPlayground {
    private static final JsonFactory JSON_FACTORY = GsonFactory.getDefaultInstance();

    private static final List<String> SCOPES = Collections.singletonList(GmailScopes.GMAIL_MODIFY);
    private static final String CREDENTIALS_FILE_PATH = "google_client_secret.json";

    private static Credential getCredentials(final NetHttpTransport HTTP_TRANSPORT) throws IOException {
        try(InputStream in = new FileInputStream(CREDENTIALS_FILE_PATH)) {
            GoogleClientSecrets clientSecrets = GoogleClientSecrets.load(JSON_FACTORY, new InputStreamReader(in));

            GoogleAuthorizationCodeFlow flow = new GoogleAuthorizationCodeFlow.Builder(
                HTTP_TRANSPORT, JSON_FACTORY, clientSecrets, SCOPES)
                .setAccessType("offline")
                .build();
            LocalServerReceiver receiver = new LocalServerReceiver.Builder().setPort(8880).build();
            return new AuthorizationCodeInstalledApp(flow, receiver).authorize("user");
        }
    }

    public static void main(String[] args) throws IOException, GeneralSecurityException {
        final NetHttpTransport HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
        Credential credentials = getCredentials(HTTP_TRANSPORT);

        System.out.printf("AccessToken:\n%s\n\nRefreshToken:\n%s\n%n",
            credentials.getAccessToken(), credentials.getRefreshToken());
    }
}