title: session id cookie in gwt rpc
body: <p>Assuming I'm rolling my own session code, what's the right way to generate a unique and secure session id cookie in java.</p>
  
  <p>Should I not be rolling my own but using something that's already been standardized?</p>
  
  <p>I'm using gwt and the google app-engine platform.</p>
  
  <p>How do I make sessions persist across browser/server restarts?</p>