Sometimes, HTTP repositories are protected by htaccess with htpasswd/ldap/sql login//password.
Would it be possible to detect when GIT returns a login prompt, and forward it to the console, so user can set it and allow sources to be downloaded ?
Actually, it just forwards a "fatal: Authentication failed".
Normally it should detect this and prompt you, but maybe only for github at the moment.
This should be addressed by #1162 btw - not merged yet though.
This has been fixed a while back, both for git repos and composer repos.