How to call secure endpoint from Commerce Cloud storefront without exposing credentials?

Summary:

Use case is for our OSF application (storefront) to be able to call into our companies enterprise system to collection information on the user for specific actions. This system has an exposed REST API that is secured via SSL.

Content (required):

In order to contact our system we created an SSE that houses the SSL and authenticates fine. We would now like to implement some security on our SSE, that allows our OSF app to contact the SSE, but not any other systems for security reasons.

I have searched all of the SSE documentation I could find in docs.oracle.com as well as here on customer connect, and I have yet to see anything that does not use an out of the box webhook that supplies any kind of authentication mechanism.