Summary:
ESP (Edge Security Pack) can be used to log connections to a virtual service by Client Source IP address, even if ESP is not used for user authentication.
Details:
Enable ESP on the relevant virtual service and under ESP logging enable "Connection". Then Set Client Authentication mode to "Delegate to server" (in previous firmware this is "none") and enter your "Allowed Virtual Hosts, multiple hosts can be specified, using space-separated.
Under "Allowed Virtual Directories" use "/*".
This means all requests will be pre-excluded and therefore passed to the server. However, the option under ESP logging will ensure all connections are logged by the Client IP address.
Logs can be viewed under
Logging Options > Extended Log files > ESP Connection Log.
Those options don't appear to be available for me.