Basic Authentication is the standard, out of the box authentication mechanism for SOAP Requests into ServiceNow. A few months ago I ran into a scenario where a customer wanted to maintain a "Restricted Users" list for SOAP connections. They had assigned a specific user for their MID Server and they only wanted that user to authenticate from the MID Server itself. If a user wasn't on the "restricted" list, they could connect without regard to location.I report on this account to demonstrate how to customize your Basic Authentication mechanism in ServiceNow to provide custom filtering on SOAP and other non-interactive requests to your instance...Read more here:

Limiting ServiceNow Basic Authentication