Also known as MSAuth.
Run this using go run ., and put nmconew.ini in your Maple installation folder. Then, put the ip address / hostname in the nmconew.ini. Start game, login (see that request ends up in NMServer) and have fun.
Original release was on RaGEZONE in 2016. Link: http://forum.ragezone.com/f921/msauth-private-servers-1089817/