about witch way do i log or show the IP of players as they log ins to me game?

as my game will make no use of byond KEYs.. instead it will have you type your name then password.. so as any key can log into any char. the reason i need to find ones IP is so i can identify the computers as they log.. not just the key or char.. this will have me to reduce Similplay(like multiplay but where more than one player is allowed but not at the same time.) without the problem of having new keys created for this use.

world << Ip Addy Eh?