Java Servlet - Servlet OAuth Examples

package com.logicbig.example;

import com.google.api.client.googleapis.auth.oauth2.GoogleIdToken;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.io.IOException;

@WebServlet(urlPatterns = {"/login"})
public class LoginServlet extends HttpServlet {
    @Override
    protected void doPost (HttpServletRequest req,
                        HttpServletResponse resp)
                        throws ServletException, IOException {

        resp.setContentType("text/html");

        try {
            String idToken = req.getParameter("id_token");
            GoogleIdToken.Payload payLoad = IdTokenVerifierAndParser.getPayload(idToken);
            String name = (String) payLoad.get("name");
            String email = payLoad.getEmail();
            System.out.println("User name: " + name);
            System.out.println("User email: " + email);

            HttpSession session = req.getSession(true);
            session.setAttribute("userName", name);
            req.getServletContext()
               .getRequestDispatcher("/welcome-page.jsp").forward(req, resp);

        } catch (Exception e) {
            throw new RuntimeException(e);
        }
    }
}

package com.logicbig.example;

import com.google.api.client.googleapis.auth.oauth2.GoogleIdToken;
import com.google.api.client.googleapis.auth.oauth2.GoogleIdTokenVerifier;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.jackson.JacksonFactory;

public class IdTokenVerifierAndParser {
    private static final String GOOGLE_CLIENT_ID = "---- use your google Client ID here-----";

    public static GoogleIdToken.Payload getPayload (String tokenString) throws Exception {

        JacksonFactory jacksonFactory = new JacksonFactory();
        GoogleIdTokenVerifier googleIdTokenVerifier =
                            new GoogleIdTokenVerifier(new NetHttpTransport(), jacksonFactory);

        GoogleIdToken token = GoogleIdToken.parse(jacksonFactory, tokenString);

        if (googleIdTokenVerifier.verify(token)) {
            GoogleIdToken.Payload payload = token.getPayload();
            if (!GOOGLE_CLIENT_ID.equals(payload.getAudience())) {
                throw new IllegalArgumentException("Audience mismatch");
            } else if (!GOOGLE_CLIENT_ID.equals(payload.getAuthorizedParty())) {
                throw new IllegalArgumentException("Client ID mismatch");
            }
            return payload;
        } else {
            throw new IllegalArgumentException("id token cannot be verified");
        }
    }
}