Answer
IP whitelisting at the network/ingress level (restricting traffic to /admin so it's only accepted from the jump host's or app server's own IP) is the supported approach here, since /admin can't be isolated onto its own port the way the Middleware/MWS Console can. IFS's own security documentation on exposing the application to the internet covers this kind of network-level access restriction and is the right starting point for setting it up correctly.