It will work like so:

 

Person1 logs in as "User1" and writes tag "Person1:User1"

 

Person 2 comes along and logs in as "User1" - while logging in - it will detect that Person1:User1 already logged in and will kick him out by sending push notification. Person1 in fact may be out already, but if not - he will get notification that someone with same login just connected and he is being pushed out.

 

This kind of stuff will be obvious for users and they will buy licenses if that is a main point :)

 

 

 

Here's some info on hooking into the window unload:  http://mark.mymonster.nl/2009/02/28/integration-of-browsers-unloading-with-silverlight/ 

 

 

DevForce itself doesn't provide this, but you should be able to do what you need within your custom IEntityLoginManager.   An instance of your login manager is constructed by an EntityServer when it starts, so you can keep your own state for the lifetime of the EntityServer.   Since a login manager implements both Login and Logout methods you can add and remove the user from your own list or dictionary, and check this to restrict access.  The only real way to fail a login is to throw a LoginException (or a custom sub-type of it), but what you throw in your login manager will flow back to your client application.