HTTP Request to SharePoint 2013 API with HTTPOnly Cookie

I need to be able to send HTTP requests to a SharePoint 2013 API whose frontend is behind a PKI authentication. I’ve attempted using the built in HTTP Request activity, but the requests get denied unless I enter in an HTTPOnly cookie. I’m currently getting this cookie from the Dev Tools and manually setting its value in the cookies field.

I’ve also attempted logging into the site and sending the HTTP request with Inject JS via the fetch request code below:

    function(element, input) {
      var splitInput = input.split(',');
      var response = fetch("https://myurlendpoint)", {
        method: 'POST',
        credentials: 'include',
        headers: {
          'Accept': 'application/json;odata=verbose',
          'Content-Type': 'application/json;odata=verbose',
          'X-RequestDigest': splitInput[0] + ',' + splitInput[1]
        body: splitInput[2]
      .then(resp => resp.json())
      .then(data => data);

      return response;

This successfully POSTs files to my endpoint, but I can’t find a way to make the JavaScript asynchronous in order to see the response from the server. The ScriptOutput of the JS Inject is always [object Promise], which is problematic to verify requests successfully went through or for any GET requests.

I wanted to see if anyone had solutions to either of these missing links for my process, or if there is another route? Otherwise, my current idea is to attempt the bot emulating the HTTPOnly cookie parsing from the Dev Tools.

Thank you for any help!