based on this: https://coolaj86.com/articles/vanilla-devops-git-credentials-cheatsheet/
I'm making it possible to authenticate to github repos from executable scripts
The main intended use for this is to support private repos on https://github.com/mshanemc/deploy-to-sfdx but it's a buildpack so use it for whatever you like.
Get a github personal access token
Set up a heroku environment variable
GITHUB_PAT to be your token