My current setup with the company i\'ve joined is IIS is being used as our main web server, using a CA signed certificate. I\'ve got access to the certificate.pdx aswell as
It would be best if the IIS could proxy the requests to your Node app. That way your Node app wouldn't even need a certificate (if it's on localhost). See this answer for more details:
It uses the example of nginx but you should be able to proxy the requests with IIS as well. See this tutorial: