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
Set Git credential.helper to wincred.
git config --global credential.helper wincred
Make sure there is only 1 credential.helper
git config -l
If there is more than 1 and it's not set to wincred remove it.
git config --system --unset credential.helper
Now set the proxy with no password.
git config --global http.proxy http://@proxy:80
Check that all the settings that you added looks good....
git config --global -l
Now you good to go!