I created the private repo examplesite/myprivaterepo using the Github UI from my browser.
Then I went to my go directory (on the desktop) and cloned it:
I had the same problem on windows "error: failed to execute prompt script (exit code 1) fatal: could not read Username for 'https://github.com': No error" trying to login to github through the login dialog. When I canceled the dialog git asked me for login and password in the command line and it worked fine.