varnish.php

<?php
class  plgSystemVarnish extends JPlugin
{
  function onAfterRoute( )
  {
    $user = JFactory::getUser( );
    $option = JRequest::getVar( 'option' );
    if( !$user->guest || $option == 'com_users' )
    {
      setcookie( 'varnishbypass', 'True', time( ) + 604800, '/' );
    }
    else
    {
      setcookie( 'varnishbypass', '', time( ) - 604800, '/' );
    }
  }
  // setting the cookie in the afterRoute event is probably adequate,
  // but in an outburst of belt and braces I decided to set/unset the
  // cookie on the log in and out events too. Probably unnecessary,
  // but apparently harmless.
  function onUserLogin( $response )
  {
    setcookie( 'varnishbypass', 'True', time( ) + 604800, '/' );
  }
  function onUserLogout( $response )
  {
    setcookie( 'varnishbypass', '', time( ) - 604800, '/' );
  }
}