Hello Charles
It is possible to configure syslog messages to be sent when the user connects and disconnects. There are various kinds of connections that can be logged including anyconnect/ssl vpn clients.
For VPN client based connections like AnyConnect, the syslogs are usually of the form 722xxx. For example, connect is 722022 and disconnect is 722023. You can find additional related messages here:
As for the configuration of the logging, this can be done either with command line or ADSM configuration methods. Take a look at the following link which includes aspects of both of these options:
I hope this has been helpful to get you started.
Laz