I have this GWT application which login/logout to a server.
The server side is ok as it can login/logout a connection.
However I need that when the application login in with a browser, the application will stay logged in for each new instance of the application.
You could store the information if a user has been successfully authenticated in the http session on the server side and provide a service like
which checks that property.
Before showing any sensitive information in the client, call that service to make sure, the current user is authenticated. I would recommend not to store login credentials in a cookie.