Applying access list for the web management console.
This can be done only on CLI with the command below:
(config)# web-management access-list <IP address>/<prefix length>
There is no error message but when applying the access list, it also restricted the access to SSH and SNMP access as well where in the CLI documentation, it does not stated that SSH and SNMP will be affected as well.
This is by design and the issue is more to not mentioned it in the document below:
Integration between CAS and ProxySG.
The document will be updated.