Altering the backend response

Here we override the TTL of a object coming from the backend if it
matches certain criteria::

  sub vcl_backend_response {
     if (bereq.url ~ "\.(png|gif|jpg)$") {
       unset beresp.http.set-cookie;
       set beresp.ttl = 1h;
    }
  }



We also remove any Set-Cookie headers in order to avoid creation of a
`hit-for-miss` object. See :ref:`vcl_actions`.