Furthermore, if in the same Jenkins project we need to checkout several private GitHub repositories into several separate dirs under a project root. How can we do it please?
The Jenkin's Multiple SCMs Plugin has solved the several repositories problem for me very nicely. I have just got working a project build that checks out four different git repos under a common folder. (I'm a bit reluctant to use git super-projects as suggested previously by Lukasz Rzanek, as git is complex enough without submodules.)