Hello @JiaTang ,

Once you create a service instance, it shows the options in this space under ‘Service Authentication’.  Example image shown below:

Also, this might help: https://help.nintex.com/en-US/nintexautomation/userguide/5.7/Content/K2-Management-Site/Integration/SmartObjectAdministration.htm?tocpath=Administer%7CManagement%7CIntegration%7C_____0 

Hi @JiaTang , can you perhaps elaborate on what you are trying to achieve?

Security is highly dependant on the Service Type.

Some can use windows credentials, others require OAuth, other Basic Auth etc. etc.

This feature is only available in 5.6 or later, so if you are on older versions, service instance and type security is not available.