Providing a “Sign-in with Google” functionality using Scala

https://accounts.google.com/o/oauth2/auth?
scope=https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fuserinfo.email+https%3A%2F%2Fwww.googleapis.com%2Fauth%2Fuserinfo.profile&
state=%2Fprofile&
redirect_uri=https%3A%2F%2Foauth2-login-demo.appspot.com%2Foauthcallback&
response_type=token&
client_id=812741506391.apps.googleusercontent.com

/**
   * Dispatch requests for twitter. We are interested in
   * twitter/authenticate, twitter/callback and twitter/logout
   */
  def matcher: LiftRules.DispatchPF = {
    case req @ Req("google" :: "authenticate" :: Nil, _, GetRequest) =>
      () => signUpRedirect(req)
    case req @ Req("google" :: "catchtoken" :: Nil, _, GetRequest) =>
      () => processCallBack(req)
  }

  /**
   * Calls Google API to authenticate the user.
   * Post authentication Google would send the token back on callbackURL
   * @See OAuth2 with Google https://developers.google.com/accounts/docs/OAuth2UserAgent
   */
  def signUpRedirect(req: Req): Box[LiftResponse] = {
    val callbackURL = req.hostAndPath + "/google/callback"
    val url = new GoogleBrowserClientRequestUrl(Props.get("google.client.id").openOr(""),
      callbackURL, Arrays.asList("https://www.googleapis.com/auth/userinfo.email", "https://www.googleapis.com/auth/userinfo.profile")).
      setState("/").build()
    S.redirectTo(url);

  }

LiftRules.dispatch.append(GoogleDispatcher.matcher)

https://oauth2-login-demo.appspot.com/oauthcallback#access_token=1/fFBGRNJru1FQd44AzqT3Zg&token_type=Bearer&expires_in=3600

//Google menu
  val googleCallback = MenuLoc(Menu.i("GoogleCallback") / "google" / "callback" >> Hidden)

<script type="text/javascript" language="javascript">// <![CDATA[
	// First, parse the query string
	var params = {}, queryString = location.hash.substring(1), regex = /([^&=]+)=([^&]*)/g, m;
	while (m = regex.exec(queryString)) {
		params[decodeURIComponent(m[1])] = decodeURIComponent(m[2]);
	}

	// And send the token over to the server
	var req = new XMLHttpRequest();
	// consider using POST so query isn't logged
	req.open('GET', 'http://' + window.location.host + '/google/catchtoken?'
			+ queryString, true);

	req.onreadystatechange = function(e) {
		if (req.readyState == 4) {
			if (req.status == 200) {
				window.location = params['state']
			} else if (req.status == 400) {
				alert('There was an error processing the token.')
			} else {
				alert('something else other than 200 was returned')
			}
		}
	};
	req.send(null);
// ]]></script>

 case req @ Req("google" :: "catchtoken" :: Nil, _, GetRequest) =>
      () => processCallBack(req)

/**
   * Call back from Google post authentication.
   * Login the authenticated user or 'create and login' new user.
   */
  def processCallBack(req: Req): Box[LiftResponse] = {

    // fetch user info object form Google
    val userInfo = validateTokenAndFetchUser(req)

    // process the obtained user information
    createOrLoginUser(userInfo)
    S.redirectTo("/")
  }

  /**
   * Using Google client libraries to fetch the information.
   * @See http://stackoverflow.com/questions/11328832/how-to-validate-google-oauth2-token-from-java-code
   */
  private def validateTokenAndFetchUser(req: Req) = {
    val transport = new NetHttpTransport()
    val jsonFactory = new JacksonFactory()
    val accessToken = req.param("access_token").open_!
    val refreshToken = req.param("access_token").open_!

    // TODO GoogleAccessProtectedResource is marked as deprecated, need to check the alternate
    val requestInitializer = new GoogleAccessProtectedResource(accessToken, transport, jsonFactory,
      Props.get("google.client.id").openOr(""), Props.get("google.client.secret").openOr(""), refreshToken)

    // set up global Oauth2 instance
    val oauth2 = new Oauth2.Builder(transport, jsonFactory, requestInitializer).setApplicationName("Knoldus").build()

    oauth2.userinfo().get().execute()

  }

  /**
   * If the user exists then login else create user.
   */
  private def createOrLoginUser(userInfo: Userinfo) = {
    User.findByEmail(userInfo.getEmail) match {
      case Full(user) => // needs merging
        User.logUserIn(user, true, true)

      case _ => // new user; send to register page with form pre-filled
        val user = User
        User.id(new ObjectId)
        user.name(userInfo.getName)
        user.email(userInfo.getEmail)
        user.username(userInfo.getEmail)
        user.verified(userInfo.getVerifiedEmail)
        user.save
        User.logUserIn(user, true, true)
    }
  }