1st -- go get
will refuse to authenticate on the command line. So you need to cache the credentials in git. Because I use osx I can use osxkeychain credential helper.
2nd For me, I have 2FA enabled and thus could not use my password to auth. Instead I had to generate a personal access token to use in place of the password.
git clone https://github.com/user/private_repo
and used your github.com username for username and the generated personal access token for password.Removed the just cloned repo and retest to ensure creds were cached -- git clone https://github.com/user/private_repo
and this time wasnt asked for creds.