bool
    invalidate(int $lifetime = null)
         
 Invalidates the current session. Clears all session attributes and flashes and regenerates the session and deletes the old session from persistence. 
 Parameters int $lifetime Sets the cookie lifetime for the session cookie. A null value will leave the system settings unchanged, 0 sets the cookie to expire with browser session. Time is in seconds, and is not a Unix timestamp. Return Value bool True if session invalidated, false if error