I have a Squid server and I think that many accounts should be deleted because people are simply not using the account anymore or they quit job ages ago...
How can I obtain a list with the last login date so I can decide which user delete?
From the Squid point of view, the only way to see that is using the access.log. Set the logrorate to the number of days that you want to track and after those days check if the user appears in the log file.
May be the information exists in your authentication backend whatever it is.