Using Private Git Repos/Submodules With Cloudflare Pages

I ran into some trouble trying to use a Git submodule to isolate content from my config and share it across multiple sites with the same static site generator. The key to solving my issue was using the ssh url ([email protected]:username/project.git) instead of the https url (https://github.com/username/project.git) when adding the submodule to my project. That made all the difference!