title: extract value of a query parameter in varnish
body: <p>I have this url:</p>
  
  <p><code>http://my.api.com/v1/{api_key}/{user_token}/?someparam=hello&amp;force=true&amp;someotherparam=world</code></p>
  
  <p>where <code>api_key</code> and <code>user_token</code> are uuids</p>
  
  <p>How do I extract the value of the <code>force</code> query param, and either do a lookup from varnish cache if the force param is missing OR it is set to false. If it is set to true, I need to hit my backend server. Query params can be in any order.</p>