Extension to external system in Order Managment

We want to create an Order Management extension that connects to an integration via SOAP or API service and returns a response. We've already created several extensions to OIC via SOAP and API services, but we always end up getting a 401 authentication error even though we're sending the credentials in the payload. I have several questions about this:

1. Is it possible for an extension to connect to an external system via SOAP or API?
2. If so, do the credentials have to be sent in the payload, or is there another way to do it? I send it in the payload via SOAP UI and it connects to the integration without issue, but using the extension, I get a 401 error.