How to only allow API Request from SSL certified site?

Hi all,

I am exploring the Sage 300 Web API. I am making a POST request from an e-commerce site, to insert AR invoice batches. I notice that the site with 'Connection not secure' can make a request to Sage 300 API as well. How can we restrict these unsecured website from making API requests to Sage 300 API?

Thank you.