Note: while the use-case described is about using submodules within a project, the same applies to a normal git clone of a repository over HTTP.
I have
Worth to mention: Most examples on the net show examples like
git config --global http.proxy proxy_user:proxy_passwd@proxy_ip:proxy_port
So it seems, that - if your proxy needs authentication - you must leave your company-password in the git-config. Which isn't really cool.
But, if you just configure the user without password:
git config --global http.proxy proxy_user@proxy_ip:proxy_port
Git seems (at least on my Windows-machine without credentials-helper) to recognize that and prompts for the proxy-password on repo-access.