I presume you have the database setup and everything working except the hauthd proxy.
in database lin2db in server table, add for example 3 server for testing purposes. (change IPs to mach yours)
server1: id = 1, name = proxy1, ip = x.x.x.x, inner_ip = 192.168.1.2, ageLimit = 0, pk_flag = 1, kind = 0, port = 7777, region = 1
server2: id = 2, name = proxy2, ip = y.y.y.y, inner_ip - 192.168.1.2, ageLimit = 0, pk_flag = 1, kind = 0, port = 7777, region = 1
server3: id = 3, name = proxy3, ip = z.z.z.z, inner_ip - 192.168.1.2, ageLimit = 0, pk_flag = 1, kind = 0, port = 7777, region = 1
name can be anything you like
change x.x.x.x, z.z.z etc ... to the proxy ips, eressea already posted a great guide about that
change inner_ip to your internal network.
save that and open hAuthD.ini, go to [Adv] section and add this line ServerEndpoints = 3
save the file.
start hAuthd
in l2server.ini [AuthD] section put
address="192.168.1.2"
start l2server.exe
see if it works