Windows Username to SSID and Reverse
From KlavoWiki
Username to SSID
wmic useraccount where name="my-username" get sid
SSID to Username
wmic useraccount where sid='S-1-2-12-44444444-5555555555-6666666666-777777' get name
Note : Expect to wait 5 or 10 minutes (possibly longer) for a result depending on the size of your domain.