How to: Using Private Git Repository
You can use `Personal Access Tokens` for Build Contexts from Private
Repositories from
[GitHub](https://blog.github.com/2012-09-21-easier-builds-and-deployments-using-git-over-https-and-oauth/).

You can either pass this in as part of the git URL (e.g.,
`git://TOKEN@github.com/acme/myproject.git#refs/heads/mybranch`) or using the
environment variable `GIT_TOKEN`.

You can also pass `GIT_USERNAME` and `GIT_PASSWORD` (password being the token)
if you want to be explicit about the username.