Building from a private mercurial repo?

Hello all,

I was wondering if anyone has had any success trying to build from a private mercurial repo. To my understanding, private git repos are a non-problem because Nix is able to obtain a username/password from local state. If this is also the case for mercurial, it isn’t working for me - I’m trying to use the fetchhg fetcher, and being told that authentication is required.

Any help/thoughts appreciated.