Hi,
To perform a login you have to use Joomla, because it's related to Joomla.
But I think that the best will for you will be to have an option to target the serial user instead of the logged user.
So I added a new option in the plugin for the next HikaSerial release.
The idea is to check the new setting during "onBeforeSerialConsume" and to load the user link to the serial during "onAfterSerialConsume", then depending the new setting, we pass the logged user or the linked user to the function "givePoints".
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.