- No need to set the mode here. The default `0644` is fine.
- The path could come from capability as for other components.
- `s/sudo/git/` ;)

Have you tested that appending always works? Now every `vagrant provision` adds a new `[http]` section and `proxy` key. I assume git is fine with that? And if the value is empty, does it reset the setting for git? Sorry, I'm lazy to check myself before asking. :)