HAProxy+Varnish configuration advice

I am using HAProxy to load balance a bunch of PHP servers and want to introduce Varnish in the scene now.
HAP sends request to Varnish iff app-login cookie is not available, Varnish doesnt have to do anything here except to serve request(Cache HIT) or send it back to HAP incase of Cache MISS, HAP then selects a PHP server & resources are fetched from it and served to client by HAP through Varnish. I have the following config file.
I don't understand 2 things here;

1. in cache miss scenario varnish gives request back to HAP which checks for the app-login cookie, doesn't find it and sends it back to varnish (end less loop situation), I can have Varnish set a cookie and make HAP to check for that and select PHP servers backend on this basis(suggestions welcome).
2. Secondly, how can I achieve that when resources are fetched by HAP in case of MISS it sends to varnish and then it is served to client , this way Varnish builds up the cache eventually.

Please also let me know if some thing critical is missed out here.

Thanks in advance

Config File

#BE for Varnish is HAP in this machine 
backend default {
.host = "127.0.0.1";
.port = "80";
}

sub vcl_recv {
# HAP sends request to Varnish iff app-login cookie is not available
# Varnish doesnt have to do anything here except to serve request(Cache HIT) or
# send it back to HAP incase of Cache MISS, resouces are then fetched from PHP servers 
# and served to client by HAP through Varnish

# We unset the cookies here as they dont affect the response
 unset req.http.cookie;
# Lighttpd is already compressing resources, so we dont do it here.
 return (lookup); # Control is passed to vcl_hit or vcl_miss 
}
sub vcl_hit {
 return (deliver);
}

sub vcl_miss {
 return (fetch);
}

sub vcl_fetch {
  set obj.ttl = 1m;
  return (deliver);
}

sub vcl_deliver {
 if (obj.hits > 0) {
            set resp.http.X-Cache = "HIT";
    } else {
            set resp.http.X-Cache = "MISS";
    }
 return (deliver);
}

sub vcl_init {
  return (ok);
}

sub vcl_fini {
   return (ok);
}