Verify the server socket in cjdroute is open:
$ netstat -l |grep 11234
tcp 0 0 localhost:11234 *:* LISTEN
Start the server:
/cjdns$ build/admin/http/HttpServer 127.0.0.1:11234 `pwd`/admin/http/
Verify it bound to a port:
$ netstat -l |grep 51902
tcp6 0 0 [::]:51902 [::]:* LISTEN
You should be able to use SSH port forwarding to access the port on a headless server: Go to this URL on your workstation, once the ssh-port-forward to the server is made http://127.0.0.1:51902