There are two options to clone a git repository from github: git over ssh or https.
Cloning via https requires either your github login credentials or a github access token in
$HOME/.gitconfig. When using git over ssh you authenticate with your ssh key.
By default, go uses https to clone repositories from github when you run e.g.
go get github.com/kubernetes/kubernetes. So for cloning private repositories that means I somehow had to authenticate with github in a way I described above. The same was necessary to push into any repository (public or private).
What I ended up most of the time was either cloning my private repositories manually (via git over ssh) or manually changing the remote locations of repositories I downloaded via
go get to use git over ssh. I was not satisfied with either options so I was extra happy when I was told about this little bit you can put in
[url "firstname.lastname@example.org:"] insteadOf = https://github.com/
With this configuration, every time you clone something from a repository starting with
https://github.com/ git automatically uses