class UserController {
    def logout() {
        log.info "User agent: " + request.getHeader("User-Agent")
        session.invalidate()
        redirect(action: "login")
    }
    def login() {}
}session
Purpose
The session object is an instance of the Servlet API’s HttpSession class
Examples
Description
The HttpSession class is useful for associated session data with a client.
Session attributes which are normally accessible from the getAttribute can also be indexed into using the array index operator or de-reference operator:
def user = session["user"]
session["user"] = "John"
assert "John" == session.user