Add login with Facebook, login with PayPal to an existing Java/Struts website

An existing web application needs "sign up with Facebook", "sign up with PayPal" functionality. The web app is written in Java, Servlet 3.0, Struts 2, JSP, container managed form based authentication. Check out the app code, learn the architecture, add or modify JSP pages, Struts Actions. The new sign up page will have two more buttons: "sign up with Facebook", "sign up with PayPal". Upon successful sign up, user data retrieved from Facebook or PayPal and facebookId (or PayPal id) should be persisted with the user account. Use existing libraries for persistence and business logic. The login page is to have the new "login with ..." buttons, use a new Struts Action for login and use Servlet 3.0 login() functionality instead of the standard container form-based authentication. The work is to be supervised by a senior developer, available by phone and chat in the UTC-05:00 time zone. Language: English, Russian. Will promptly answer any questions related to the app architecture to speed up the learning process. We have more work in this project and are looking for a long term enagement upon successful completion of this task. When posting a response please mention in the first line 11th and 12th significant digits in the number Pi.