Is it possible to use pip to install a package from a private GitHub repository?

You can use the git+ssh URI scheme, but you must set a username. Notice the git@ part in the URI:

pip install git+ssh://git@github.com/echweb/echweb-utils.git

Also read about deploy keys.

PS: In my installation, the "git+ssh" URI scheme works only with "editable" requirements:

pip install -e URI#egg=EggName

Remember: Change the : character that git remote -v prints to a / character before using the remote's address in the pip command:

$ git remote -vorigin  git@github.com:echweb/echweb-utils.git (fetch)#                     ^ change this to a '/' character

If you forget, you will get this error:

ssh: Could not resolve hostname github.com:echweb:         nodename nor servname provided, or not known

As an additional technique, if you have the private repository cloned locally, you can do:

pip install git+file://c:/repo/directory

More modernly, you can just do this (and the -e will mean you don't have to commit changes before they're reflected):

pip install -e C:\repo\directory

You can do it directly with the HTTPS URL like this:

pip install git+https://github.com/username/repo.git

This also works just appending that line in the requirements.txt in a Django project, for instance.