Google OAuth 2.0 on Google App Engine Standard with Java 11

This sample shows how to implement an OAuth 2.0 flow using the Google OAuth Client Library for Java to access protected data stored on Google services. OAuth 2.0 is a standard specification for allowing end users to securely authorize a client application to access protected server-side resources.

Setup you Google Cloud Project

Make sure gcloud is installed and initialized:

   gcloud init

If this is the first time you are creating an App Engine project

   gcloud app create

Setup the Sample App

Copy the sample apps to your local machine:

  git clone https://github.com/GoogleCloudPlatform/java-docs-samples

Add the appengine-simple-jetty-main Main class to your classpath:

  cd java-docs-samples/appengine-java11/appengine-simple-jetty-main
  mvn install

In the Cloud Developers Console > API Manager > Credentials, create a OAuth Client ID for a Web Application. You will need to provide an authorized redirect URI origin: https://<PROJECT_ID>.appspot.com/oauth2callback.
Replace CLIENT_ID and CLIENT_SECRET with these values in your app.yaml
Move into the appengine-java11/oauth2 directory and compile the app:

  cd ../oauth2
  mvn package

Deploy to App Engine Standard

mvn clean package appengine:deploy -Dapp.deploy.projectId=<your-project-id>

To view your app, use command:

gcloud app browse

Or navigate to http://.appspot.com URL.