"We are trying to determine current license capacity of the device."
Hi Erik,
if that's all you want, there is no need for the hassle of measuring actual connections. Just do:
sh ver
and the ASA will tell you about the license capacity regarding SSL VPNs (and then some).
Anyway, say that you get that number, and you are not sure whether the capacity will suffice, then you'd probably want to measure actual connections over time. The most straightforward way I can think of is using SNMP. Do:
sh snmp-server oidlist
and you'll get the full list. SSL VPN ("Web VPN") starts at 1.3.6.1.4.1.9.9.392.1.3.38. on the ASA I looked at, and you can poll number of current sessions, number of cumulative sessions, and number of sessions at the peak.
Best,
Johnny