K2 Smartobject Service authentication

Hi All!

I've successfully configured the Smartobject Services with this guide:

https://help.nintex.com/en-US/k2blackpearl/DevRef/4.7/default.htm#Windows_Authentication_with_SSL_for_K2_SmartObject_Services.html%3FTocPath%3DReference%2520Information%7CServices%2520Reference%7CSmartObject%2520Services%7CConfiguration%7C_____1

How can I set only one dedicated user reach the endpoints, not everyone who is in the domain (AD). I want only the K2 service user has an access.

Thanks

Laszlo