Not sure about this one. [I think it's just the User-Agent](https://github.com/alphagov/pp-puppet/blob/master/modules/varnish/templates/default.vcl.erb#L14) that [I put in for debugging purposes](https://github.com/alphagov/pp-puppet/commit/6029a7da083a5878efa38cac77eea6f8aedae1f7) and potentially could be spoofed by external requests.