I saw your http://www.seamframework.org/Community/LoginUserAtMostOnceTime thread and I'm going try to help (but I'm new to seam as well).

AFAIK seam doesn't have anything to support this, you have to implement it.

To archive this you need to keep a List with all logged users in application scope with the UserID and SessionID and prevent the user to log in again if the UserID is already stored in the List (on Application Scope).

But you have to implement a way to the user override the sessionID stored on the application scope to a new one because the hardest part to prevent the user log in with another browser, workstation, etc is how to handle the log out because the browser is not connected with the web server.

If the user don't log out of your application they will won't be able to log in again until any expiration mechanism take care.

To add a user to the Application Scope you can use the seam loginSuccessful event.
To remove the user when he log out you can extend seam Identity class and override the logout method.
To expire i guess the best way is to create a POJO servlet that implements HttpSessionBindingListener interface (you can google it for examples).

Hope this help.

Cheers, Andre.

FacesContext facesContext = FacesContext.getCurrentInstance();
Object target = context.getExternalContext().getApplicationMap().get("nameOfYOurObjectWhen YouStoreOnTheMap");

Example

MyCustomObject object = new MyCustomObject();
FacesContext facesContext = FacesContext.getCurrentInstance();
context.getExternalContext().getApplicationMap().put("toApp", object);
MyCustomObject object = (MyCustomObject)context.getExternalContext().getApplicationMap().get("toApp");

Regards.

I don't know either how to access the way you want.
But I guess you can invalidate the desired session in a Servlet Filter when the request arrives.
For this this create a new Map in the Application Context and just check if the ID of the current request is invalid in the List.

Example:

public class invalidateSession extends HttpServlet {

  public void doGet(HttpServletRequest req, HttpServletResponse res)
                               throws ServletException, IOException {

    HttpSession session = req.getSession(true); // get the actual session

    if (!session.isNew()) {  // skip new sessions

        // test the actual session in the Map of the sessions to be invalidated

        session.invalidate();
    }

    // Continue processing...
  }
}