I believe it was requested for several times, so I decided to realize that for everyone because I am also interested in that.
This is simple as its called - plugin purges clientprefs database by removing player 'cookies', which has not been updated for long time.
It also refreshes cookies timestamp every time player connects, so cookies will not be removed accidentally (at least after
once it purged).
There's only one ConVar:
sm_cookies_removedays - Removes cookies which hasn't been updated for X days.
By default it removes cookies after 30 days of player inactivity.
Also don't forget to save current clientprefs database if you really care about cookies.
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