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Sessions handling in Vaadin

I have a Vaadin application that starts with a user login, but the problem is with Vaadin is the session handling as I can open two sessions from 2 different browsers with the same login which should not be possible to do. But I did not find any documentation regarding that besides this topic but it's not working properly as the data are not saved in the hashmap correctly.Anyone got the same problem?

Vaadin 7 works by default so that it creates everytime a new UI instance when a new browser tab is opened (or the tab is refreshed). You should store information about current user to VaadinSession or standard HttpSession and check in UI.init() if the session contains user information.
To store information into VaadinSession one can say:
VaadinSession.getCurrent().setAttribute("currentUser", currentUser)
HttpSession can be accessed as follows in Vaadin:
VaadinSession.getCurrent().getSession()
Please note that VaadinSessions are stored into HttpSession and HttpSession can contain multiple VaadinSessions if multiple Vaadin servlets are deployed from the same war file, and the user uses those at the same time.

How to prevent concurrent logins?
I keep track of logins using a self-generated login-token. A random string between 32 and 128 bytes in length that gets stored in a cookie and a backend database, typically under a user's account.
If User (A) shares her login credentials with User (B) a new login-token is generated for the new login and stored in a cookie and updated in the backed database.
If User (A) (who might for example already be logged in) attempts to perform an action while User (B) has just logged-in, User (A)'s session will be destroyed and she'll be redirected to the login screen after a backend test confirmed her login-token isn't a match.
Think of Sessions and Logins as two different things. Sessions can be generated all day long, but login STATE should be stored in a central store.

You can save all logged users to static Set. Static variables are globally shared. On start app, check whether the collection is already login.

Java + RestFB API: Getting fresh Page Access Token without messing with AppID, appSecret

What I want to do:
I am trying to make a simple program that posts 5-10 statuses, at a time, on a page's wall. The post to the page will have to be done under the name of the page.
I've read tons of badly written Facebook Developers documentation and I'm reaching the point of confusion where I don't even know what questions to ask. So her I am.
My code so far:
I manually got the Page Access token manually, by this method:
Go to https://developers.facebook.com/tools/explorer
At the GET request form, down there, fill in me/accounts
You'll get a Javascript representation of your basic user data. Find the page you want.
Note the access_token and id fields, we're going to use them in the code below.
Thus, after getting the page Access token manually (And the ID of the page, of course)
import com.restfb.DefaultFacebookClient;
import com.restfb.FacebookClient;
import com.restfb.Parameter;
import com.restfb.exception.FacebookException;
import com.restfb.types.FacebookType;
import com.restfb.types.Page;
import com.restfb.types.User;
/**
*
* #author dsfounis
*/
public class FacebookConnector {
/* Variables */
private final String pageAccessToken = "GOT_THIS_FROM_THE_METHOD_ABOVE";
private final String pageID = "THIS_TOO";
private FacebookClient fbClient;
private User myuser = null; //Store references to myr user and page
private Page mypage = null; //for later use. In this question's context, these
//references are useless.
private int counter = 0;
public FacebookConnector() {
try {
fbClient = new DefaultFacebookClient(pageAccessToken);
myuser = fbClient.fetchObject("me", User.class);
mypage = fbClient.fetchObject(pageID, Page.class);
counter = 0;
} catch (FacebookException ex) { //So that you can see what went wrong
ex.printStackTrace(System.err); //in case you did anything incorrectly
}
}
public void makeTestPost() {
fbClient.publish(pageID + "/feed", FacebookType.class, Parameter.with("message", Integer.toString(counter) + ": Hello, facebook World!"));
counter++;
}
}
The problem:
The code above works. The thing is, it works temporarily. The page access token that I get has an expiration time of one hour, and I need to manually go through the process of obtaining it, every time that I run the program. What is the point of automating a process if I keep some aspects of it manual?
So I have to ask you: Can I do the process above programmatically, and obtain a fresh page access token at program launch?
Can I, maybe, use a better API to do something as simple as just post a couple of things on a Page's wall, every day?
My application is a console one, and I would like to stay away from implementing needless Logins, even though if you tell me that it is needed, it's going to be a bother I'll have to go through.
As a note: I've got the application registered in Facebook Developers, albeit only as a basic app. To get more permissions, I need to show proof of Facebook Login implementation, and as I say in the title, it's something I'll have to avoid.

There is no automatic process to obtain an access token. If there was, it will defeat the whole purpose of the OAuth flow. For pet projects and tests it's okay to use the Graph API Explorer but for public applications involving users it is mandatory that the user manually selects the login dialog.
Under your current scenario you can extend the user token using the method mentioned here https://developers.facebook.com/docs/roadmap/completed-changes/offline-access-removal/
Scenario 5: Page Access Tokens
When a user grants an app the manage_pages permission, the app is able
to obtain page access tokens for pages that the user administers by
querying the [User ID]/accounts Graph API endpoint. With the migration
enabled, when using a short-lived user access token to query this
endpoint, the page access tokens obtained are short-lived as well.
Exchange the short-lived user access token for a long-lived access
token using the endpoint and steps explained earlier.
https://graph.facebook.com/oauth/access_token?
client_id=APP_ID&
client_secret=APP_SECRET&
grant_type=fb_exchange_token&
fb_exchange_token=EXISTING_ACCESS_TOKEN
By using a
long-lived user access token, querying the [User ID]/accounts endpoint
will now provide page access tokens that do not expire for pages that
a user manages. This will also apply when querying with a non-expiring
user access token obtained through the deprecated offline_access
permission.
A simple program used only by the owner of the application does not need approval from Facebook.
e.g. https://www.facebook.com/phwdbot

HttpRequest object after session times out for a web application

I wanted to know how request objects behave when a session is time out.
To be more specific I came across to one scenario, for which I am not able to figure out what is happening exactly.
The scenario is like this,
I have a login page for my web application with username and password fields. I have set the time out to 10 minutes for my app.
I am on the login page doing nothing for 15 minutes, so the session is timed out.
Now on the login I put the user name and password and hit submit. The page is getting refreshed instead of submitting.
So can I say upon session time out,the request object also times out?

Since you do not add any code to your question, my explanations should be taken with a grain of salt.
IMHO, you are starting the session when a client requests the login page (before he submits the login page) and also you've set it so that a request belonging to a timeout session will be redirected to login page.
So if the result is not to your liking you have to change some of the above.
But again, for a better answer, you have to show us some code.
And for your question about request time out. No it did not time out. It only times out if the server does not respond in time (which is a different kind of time out)
I added some Java code partials which I am using to direct requests belonging to sessions which are timed out to Login page. By the way I also should add that requests which did not require a session is handled before this redirection.
HttpSession session = request.getSession(false);
boolean hasActiveSession;
if (session == null) {
hasActiveSession = false;
//...
}
//...
if (!hasActiveSession) {
request.setAttribute("alert","Your session has timed out");
request.getRequestDispatcher("/WEB-INF/Login.jsp").forward(request, response);
}

What is a good strategy to manage sessions for beta webapplication?

I am trying to create a webapplication using Spring. The webapplication is a beta/demo site, which is invitation only. So, I need to generate a link to the webapplication url, appending a unique id, which would be valid for 24 hours. User can use that link for 24 hours and make use of the (I kind of also have plans of restricting the user by ip)
To achieve such token generation and expiry, should I just rely on the container with session time out to do it? or does it make sense to create spring backed service layer with token creation and expiry services?
EDIT
Now that I have a bounty on this to draw more attention, I thought I will rephrase the question so that it makes more sense - what would be a good strategy to force users out of a web application after a certain period of time?

Relying on session timeout would not be sufficient solution .
I am not acquaint with Spring . I would put my generic solution as below for any web application having requirement as yours :
Invitation is assumed to include a link to the Web Application .
The link is assumed to include the unique id .
The Beta/Demo user table is assumed to have a beta-expiry ( datetime ) column to hold the expiry date and time .
When your web application is accessed using the link in the invitation , update the beta-expiry column for that unique_id considering 24 hrs from then .
When a Beta/Demo user attempts to sign in , check the beta-expiry column for that particular user and allow access if the expiry is not reached . Display appropriate message in case of expiry .
Whenever a signed in Beta/Demo user performs subsequent accesses to your web application , check the beta-expiry column for that particular user and allow access if the expiry is not reached . Display appropriate message in case of expiry .
If seems useful , display a countdown timer showing the left over time somewhere in the header area .
In case of extension of Beta usage for all or a portion of users , you could update the beta_expiry column appropriately .
Additionally you could also have an invitation-expiry column to hold invitation expiry considering a particular duration for eg. a 48 hrs from when the invitation was sent .
We use a little bit similar solution to sign out ( signed in ) users from our SaaS application after a particular duration of no access .

I think that you should rely more in the back-end rather than a session on a cookie, imagine the case that you set the cookie for 24 hours expiration but the client deletes the cookies from the browser, (depending on your logic) your link will generate a new session or the request will be blocked.
IMHO you can store a session cookie on the client but you need to have a second source of comparison in the server, maybe a database, no-sql document, a collection in cache, something that you can compare and check the latest access to the client.
just to put all together imagine the following use case:
the user get the invitation link and click on it
the system check if the first time they log into the system, and save that date as a "start date" and another one as "last access"
the system sets an authentication cookie with 24 hours expiration
the system track every post back/ ajax call to the server and update "last access" date
if user deletes the cookie the system check the "last access" and make a comparison with the current server date
if valid the system creates a new auth cookie with the remaining hours
if not valid the system sends a message to the user.
for the user the cookie will expire according to the time left (calculation between start date and last access)
I hope this helps.
regards

One strategy is to keep track of expiry date-time of all the users by storing the relevant data in DB and using a cache library (to reduce DB hits while checking for the expiry date). Here is a small example:
Create a DB table with columns to map user id to expiry date: id, unique_user_id, expiry_date_time. You need to create the unique user id in your code and save it in DB before sending the URL to the user with this id. You can keep null as the initial value for expiry_date_time. Create a class to represent this mapping in Java:
class UserIdWithExpiryDate{
private String userId;
private Date expiryDateTime;
...
}
Define a Service with a cacheable method that will return an instance of this for a given userId :
public interface CacheableService {
#Cacheable("expiryDates")
public UserIdWithExpiryDate getUserIdWithExpiryDate(String id);
public void updateUserIdWithExpiryDate(String userId);
}
import org.joda.time.DateTime;
#Service
public class CacheableServiceImpl implements CacheableService {
#Autowired
private YourDao dao;
#Override
public UserIdWithExpiryDate getUserIdWithExpiryDate(String id) {
return dao.getUserIdWithExpiryDate(id);
}
public void updateUserIdWithExpiryDate(String userId){
Date expiryDate = new Date(new DateTime().plusHours(24).getMillis());
dao.update(userId, expiryDate);
}
}
The result of getUserIdWithExpiryDate method is stored into the cache so on subsequent invocations (with the same argument), the value in the cache is returned without having to actually execute the method.
Next step is to check the user's expiry date while accessing the site. This can be done using OncePerRequestFilter:
#Component("timeoutFilter")
public class TimeoutFilter extends OncePerRequestFilter {
#Autowired
CacheableService cacheableService;
// Here you need to decide whether to proceed with the request or not
#Override
protected void doFilterInternal(HttpServletRequest request,
HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
filterChain.doFilter(request, response);
}
}
Steps that can be taken inside the doFilterInternal method to check the validity of the user:
Get the user Id from request
Execute: cacheableService.getUserIdWithExpiryDate(userId)
If step 2 returns null, there is no user present with this id. You should not proceed with the request.
If step 2 returns an instance of UserIdWithExpiryDate, check the value of "expiryDateTime"
If the value of "expiryDateTime" is null,it means user is accessing the site for the first time.Update "userExpiryDate":cacheableService.updateUserIdWithExpiryDate(userId) and proceed with the request.
If "expiryDateTime" is not null, compare this with current date_time. If expiryDateTime.isAfter(currentDateTime), proceed with the request.
For caching, you can use Spring Cache Abstraction with EHCACHE.

Tokens
For this marketing purposes we generate tokens upfront, store them in a database alongside all information like restrictions to certain user account, ip ranges (for certain mobile carriers), the date and time ranges of use and so on.
In case of one time codes we just mark it as being used in the database.
To generate those codes we use Random Numbers or encode some information and use (SHA-1 or better). Then we use bigInteger.toString(36) or a different scheme and group the first 16 letters to let it look like a license key.
If we express information with it like useraccount/name or carrier (mobile) or whatever we can even validate the token without a database.
Forcing User Out
Just check for the validity of the token the first time the user starts a session or logs in. Throughout the session you just check if the token has expired (store a value in the session if you have one, append it (encrypted) in the url or whatever or check against a database.
So on every request you just check if the user has permission to access your site otherwise you block the user with an error / info page.
You can also add a java script to each page. The script can determine whether the users permission to use your site has expired by:
Encrypt the relative time that the token is valid in a hidden div and calculate the absolute time using the users local time. Then compare the absolute expire time with the user time every now and than (lets say every 3 seconds) and you can yourself all those polling and pushing (comet, ajax, websockets) behaviour.
Once the java script program notice the token has become expired remove the content sections and replace it (or mark a hidden div as visible) with the info / error page content. This way every time the user revisits pages still stored in the browser history are destroyed also. (if this is a necessity for you).
Summary
Use random tokens and a database or encrypt information (like the day the token can be used) and SHA-1.
Check the tokens validity every time the user requests a page (store the timeframe in a session / url to save roundtrips to the database)
Provide a java script that destroys local pages in the history on revisit.

Here I can think of two use cases that I have seen.
1.) This kind of management is used in applications like online tests or email verifications, where user is provided a link with some token. This link and the token is valid for some fixed period of time and can be used only once. (Ex. online tests or password reset-emails)
2.) Another use case is to provide link with a token which are also valid for a fixed period of time, but in this case the link and the token can be used any number of time within the time period allowed (Ex. Online registration forms for test or some university enrollments).
So, definitely managing this using a session only will not be a good choice as the browsers can be cleared.
So you need to maintain the pair of the link and the token at the server (May be in a DB) with some other information like last accessed time, creation date and time, Valid upto .
To be more flexible validity time for link and the token can be set differently (eg. link can be used for a set of users, but the tokens are unique to a user).
So you can use this info on every user visit to check whether the link or token is still valid and what are their last accessed time. If it turn out to be expired then you can show the relevant error message.

What about "deleting the user's account" (depends on how you are building your logging system) after 24 hours.
Coupling this with checking user's account every time (s)he loads the page, will force him/her out at the first refreshing after the 24 hours threshold passses.

You can store the id with expiration time and when a request comes in with that id check if
it's still valid
and if you are trying to accomplish something like id is valid say 5 hrs after first request then store time when the first request is made and for each subsequent request check if it's still valid

Detect user login/logout xmpp google app engine

I am using Google App Engine in Java to send XMPP messages.
I would like to know if there is a way to check if a user is logged in to the system or logged out. So, when the user signs in, I would like to send him a welcome chat message and when he signs out I would like to notify my server code of the same.
I have tried the presence API but no luck so far.

Assuming you're referring to querying a user's presence via XMPP, keep in mind that this will only work if your App Engine account is authorized by that user. If you have already got that far, querying for presence (user logged in/logged out) is quite simple (source).
If a Google talk user has subscribed to an app (has accepted an invitation or has invited the app to chat), the app can discover the user's availability by looking for a POST to /_ah/xmpp/presence/available. If the user is subscribed and available, you can send them your application's presence and status:
// In the handler for _ah/xmpp/presence/available
XMPPService xmppService = XMPPServiceFactory.getXMPPService();
Presence presence = xmppService.parsePresence(req);
// Split the XMPP address (e.g., user#gmail.com)
// from the resource (e.g., gmail.CD6EBC4A)
String from = presence.getFromJid().getId().split("/")[0];
// Mirror the contact's presence back to them
xmppService.sendPresence(from, PresenceType.AVAILABLE, presence.getPresenceShow(), presence.getStatus());
To further clarify, your app receives automatic presence notifications via the following POST URL paths:
POSTs to /_ah/xmpp/presence/available/ signal that the user is available and provide the user's chat status.
POSTs to /_ah/xmpp/presence/unavailable/ signal that the user is unavailable.
POSTs to /_ah/xmpp/presence/probe/ request a user's current presence.
As an example, when user sally logs in, you'll get a POST request to /_ah/xmpp/presence/available/ which your server will then have to process. Then when sally logs out, you'll get a separate POST request to /_ah/xmpp/presence/unavailable/.