Varnish, WordPress with preview post

vi /etc/varnish/default.vcl


backend default {
.host = "127.0.0.1";
.port = "8080";
}
# Allow posts preview
sub vcl_recv {
if (req.url ~ "preview=true") {
return(pass);
}
}
# Drop any cookies sent to WordPress.
sub vcl_recv {
if (!(req.url ~ "wp-(login|admin)")) {
unset req.http.cookie;
}
}