Remember when last logged on

It would be very helpful for XWiki to store last logon time of users. This would help answer question such as:

• What users have never logged on?
• What users are stale/dormant (e.g., haven't logged on in x days or months)?

(My experience in larger organizations suggests that security teams want to find out this kind of information.)

This could lead to good functionality for an extension (e.g., "Dormant user cleanup extension"), or be a core function.