I mostly clone GitHub and Bitbucket repositories using SSH URLs, so that I can protect this access with an SSH private/public keypair. Unfortunately, some firewalls refuse to allow SSH connections. Thankfully both GitHub and Bitbucket support using an SSH connection made over the HTTPS port. Most firewall rules should allow this – though proxy servers may still interfere.
To enable this, edit
~/.ssh/config, and add the following section:
Host github.com Hostname ssh.github.com Port 443 Host bitbucket.org Hostname altssh.bitbucket.org Port 443