title: How to work with Grails Http sessions
body: <p>I'm new to Grails and I'm struggling with sessions..</p>
  
  <p>In a controller, how do I check is the user has a valid session? In Java/Spring MVC, it's simple request.getSession(), so what's the convention in Grails?</p>
  
  <p>How do I add/get values from the session?</p>
  
  <p>Thanks,</p>