Varnish redirect based on cookie

redirect.vcl

vcl_recv {

  if (!req.http.cookie ~ "site_intro" && !req.url ~ "^/intro" && !req.http.user-agent ~ "(?i)\biPhone.*Mobile.MobileDetect") {
    error 750 "Moved Temporarily";
  }

  ...
}

vcl_error {

  if (obj.status == 750) {
    set obj.http.Location = "/intro";
    set obj.status = 302;
    return(deliver);
  }
  
  ...
}