Saving client certificate passphrase for Git over HTTPS?

I'm trying to use a remote Git repository that only provides acces开发者_如何学Pythons over HTTPS using client certificates. I've (finally...) gotten it working, but now I'm running into a minor issue -- every time I touch the remote, Git prompts me for the certificate passphrase. Obviously, this gets old fast.

If I were using SSH, I could follow the official guide to provide credentials with ssh-agent. But, AFAICT there's no way to have Git (or Curl, which is the library I think Git stubs out to under the hood) use ssh-agent to access credentials for an HTTPS connection. I'd also be fine with tying either of those two to gnome-keyring for the passphrase, but I haven't found anything about either approach online.

Can it be done? I might be able to talk the server admin into turning on SSH access, which I'm sure would sort me right out, but in the meantime it'd be easier if I could get it to save the passphrase for HTTPS.

UPDATE 2013: This was added in git 1.8.0. This question explains how to use the new gnome-keyring credential helper.