title: Output caching dynamically generated CSS
body: <p>In my application the user has the option to modify the CSS of their site.</p>
  
  <p>This is unlikely to change that often, but when it does we need to ensure that they, and their site visitors, see the results instantly.</p>
  
  <p>We do record the date and time that the user updated their CSS so an easy solution would be to just append a timestamp to the url.</p>
  
  <p>However, I would like to know if I can set the cache headers programatically to force the browser to re-request the CSS file if it changes.</p>