need custom whmcs module

we have site which give api access to create some registration keys for some service , presently we are manually processing its orders but we came to know that we have option to generate keys using api

they gave api url like this :-

http://somesite.com/?op=api_reseller...ASSWORD&t=TIME

USER = reseller username
PASSWORD = reseller account password
TIME = days, possible values: 14d 30d 90d 180d 360d 720d


i want to automate process without manual intervention so that keys generate and sent to client immediately after payment with some details, if some one can do this post here or pm me


thanks