Is it Adobe Campaign Standard (ACS) or Adobe Campaign v6/v7 ? In that latter case, please indicate your build version.
And of course, also in your firewall rules if you are On Premise hosting...
Please see the JS API documentation for the methods to call (HttpClientRequest, HttpClientResponse; or HttpSoapconnection if the Web Service called is SOAP method not REST method; etc).
You can call directly the target https url in your JS code.
If you need only to download data from an external URL inside a workflow, I recommend you to use the easiest way, define an AC external account (Administration/Platform/External Accounts, create new one, choose http type an then type your https web service url and select SSL security and if needed the credentials and port if not 443). Then in your workflow JS activity, you can use the Web Download activty, it is very easy to configure and use (even if this activity type you can define directly the URL, it is better to use external account).