Comment 1 for bug 1538651

At present it is not in general possible to build from a private repository on Launchpad using git-build-recipe. This won't be possible until we have HTTPS access tokens for private repositories (as it happens I'm working on prerequisites for that right now, but it will take a while). You can do it locally by using git+ssh://git.launchpad.net/certification-docs rather than lp:certification-docs, but it isn't going to work as part of a recipe build on Launchpad for a while yet.

I agree that the error message lacks a certain something, and will see what I can do to improve that.