To be honest I completely forgot to touch this topic in my tutorial, but here’s some insight based on my experiences with Google App Scripts.
As far as I know there are 3 ways to use third party code:
1. By interacting with the code using some kind of HTTP API (via UrlFetchApp)
2. By writing a custom GAS library. You can check my Honeybadger library if you’re curious (https://medium.com/@bajena3/google-apps-scripts-honeybadger-%EF%B8%8F-88b1df247f6a)
Not sure what exactly your code is going to do, but maybe one of the abovementioned points could be useful to you?