google oauth2 callback

        TokenResponse tokenResponse =
                new AuthorizationCodeTokenRequest(new UrlFetchTransport(),
                    new JacksonFactory(),
                    new GenericUrl("https://accounts.google.com/o/oauth2/token"),
                    this.code)
                        .setRedirectUri(Constants.googleOJCCallbackUri(
                                getContext().getRequest().getScheme(),
                                getContext().getRequest().getServerName(),
                                getContext().getRequest().getServerPort()))
                        .setClientAuthentication(
                                new ClientParametersAuthentication(
                                        Constants.GOOGLE_API_KEY,
                                        Constants.GOOGLE_API_SECRET))
                        .execute();

        Credential credential = new Credential.Builder(BearerToken.authorizationHeaderAccessMethod())
                .addRefreshListener(new CredentialStoreRefreshListener(getContext().getUser().getUserId(),
                        new AppEngineCredentialStore()))
                .setJsonFactory(new JacksonFactory())
                .setTokenServerUrl(new GenericUrl("https://accounts.google.com/o/oauth2/token"))
                .setClientAuthentication(
                        new ClientParametersAuthentication(
                                Constants.GOOGLE_API_KEY,
                                Constants.GOOGLE_API_SECRET))
                .setTransport(new UrlFetchTransport())
                .build()
                .setFromTokenResponse(tokenResponse);

        if (tokenResponse.getRefreshToken() != null) {
            log.debug("setting refresh token from token response");

            credential.setRefreshToken(tokenResponse.getRefreshToken());
        }

        AppEngineCredentialStore appEngineCredentialStore = new AppEngineCredentialStore();

        appEngineCredentialStore.store(getContext().getUser().getUserId(), credential);