I have tryed different approaches to use a Github private repository reference in a Rails application Gemfile.
1) Gemfile: gem \'my_gem\', :git
Heroku's git (version 1.7) doesn't support using e-mail as username for Github's repositories.
You must use your Github username.
Also, Heroku's git doesn't support using an oauth token.
Hopefully Heroku will upgrade their git soon, so they can continue making my life easier :-)