Hi Alan,
If you can get your administrators to open the firewall to a restricted set of IP addresses, you can whitelist the Anvil servers while still preventing connections from the rest of the internet. Contact support@anvil.works for a list of our current egress IPs (ie the IPs from which connections may emerge), which you can choose to allow through your firewall.
(Of course, those IPs are shared by multiple Anvil apps. If you want your own private egress IP, you’ll need a Dedicated plan.)