title: What Rails module or gem does set default response headers?
body: <p>With empty Rails app I have <code>Cache-Control</code> set to <code>max-age=0, private, must-revalidate</code> by default.</p>
  
  <p>I want to understand this process better so I am trying to detect code that does this job.</p>
  
  <p>I have checked <code>actionpack</code>, <code>rake middleware</code>, <code>config.action_dispatch.default_headers</code>, <code>initializers and envinronment configs</code>. </p>
  
  <p>I am using Rails 4.2, nginx as web server and Passenger as application server.</p>
  
  <p>Possibly this is some rack middleware or application server itself.</p>