How to pass customer params to git clone?

[RoxKilly]

Suppose I'm trying to download a repo using the GitGetter:

git::https://github.acme.com/team/repo

Under the hood, something like this gets executed:

git clone https://github.acme.com/team/repo /tmp/dir

The server expects me to send some extra headers. From my shell I can clone with:

git clone -c http.extraHeader='header: val' https://github.acme.com/team/repo /tmp/dir

What is the idiomatic to pass extra args to git clone (source code)?