type handler = {getpass : (unit -> Client.passwd_result) option,
adduser : {user : string, passwd : string option} -> string option,
passwd : {user : string, passwd : string} -> string option,
type handler = {getpass : (unit -> Client.passwd_result) option,
adduser : {user : string, passwd : string option} -> string option,
passwd : {user : string, passwd : string} -> string option,