First working version of the whitelist plugin. Had to modify oxmin.lua to support the passing of a plugin's context. You will need both the plugins in this gist.
Commands: /whitelist [steamid] /blacklist [steamid]
You must have canwhitelist and canblacklist flags (using the oxmin giveflag command) to run these commands. The steamid supplied can be either regular (i.e. STEAM_0:1:16556317) or steamid64 (i.e. 76561197993378363).