A "git clone git@..." command prompts the user for a password. What is the password or how is it set?
The authentication for such a git command is usually done by the individual servers not through Git itself. You should go to the server with the source repository, and run this to change the password to something you know:
sudo passwd git
Alternatively you could change the owner and group of the .git file or the permissions of the git file. Then you could set up SSH with a user on the server that has the .git repo that has permissions to access the file. To set up SSH see this posting.