Not easily. MAC address is a layer 2 artifact and the connection comes in only with layer 3/4 information (protocol, source and destination IP address and port).
The only way we can see MAC address is via something like AnyConnect ID Extensions (ACIDEX) which are exposed when using an add-on security service like Cisco Identity Services Engine (ISE). It can technically be done within an ASA or FTD config (the latter when using FMC and DAP) but I have never seen it done in my experience dealing with literally hundred of customer VPNs.
Reference: https://www.cisco.com/c/en/us/support/docs/security/anyconnect-secure-mobility-client/118944-technote-anyconnect-00.html
If you want to add a second factor to your security, use a Multi-Factor Authentication (MFA) service like Cisco Duo.
Or you could change from username/password to certificates as your authentication method. This requires a PKI though; which can be daunting to setup if you don't have one already. It's not that hard, just not something most network or security admins have experience doing.
