Michael,
In practical terms, ASA has limited capabilities to store this kind of information.
The best way to check this is on the AAA server you're using or by filtering syslogs.
ASA itself will store counters of how many authentications took place, how many succeeded etc. on a per-server basis.
Even the local server will store some info.
Example:
ASA# show aaa-server
Server Group: LOCAL
Server Protocol: Local database
Server Address: None
Server port: None
Server status: ACTIVE, Last transaction at 14:07:19 UTC Thu Oct 3 2013
Number of pending requests 0
Average round trip time 0ms
Number of authentication requests 16888
Number of authorization requests 0
Number of accounting requests 0
Number of retransmissions 0
Number of accepts 13
Number of rejects 16875
Number of challenges 0
Number of malformed responses 0
Number of bad authenticators 0
Number of timeouts 0
Number of unrecognized responses 0
Best place to get details are your syslogs and AAA server reports.
Syslog messages:
http://www.cisco.com/en/US/docs/security/asa/syslog-guide/logmsgs.html
M.
