Service Integration - Authentication is not working for web service

Service Integration - Authentication is not working for web service

I'm trying to consume a web service but it fails the authentication mechanism. In REST API Connector configuration is mentioned that an UrlConnection element is required for the Authentication property of the REST API Connector. In AUP > External Systems, I've configured correctly this system, using the username & password properties with my current credentials (username & API Key) from the third-party system.

When I test this web service from AUP, it gives me an exception related with authentication, mentioning that my security token is not found in URL. Where should I put the security token to achieve the use of my desired web service?