Support for private subrepo

I try different methods and ends up thinking that private subrepo as well as subrepo aren't well support:

• subpaths aren't use for translating subrepo alias, creating bad paths if you used the recommend way of using relative subrepo.
• even when using absolute url for subrepo, private subrepo, even personal one, aren't authenticate properly. The url is used without the x-auth-token.

Contrarely to git submodule which aren't fetch on cloning, hg subrepo are fetch on cloning, so before the bitbucket-pipeline is done. So, it's not possible to set up the ssh keys before hand.

I'm not sure if there is a good solution for this other than allowing to use deploy key from other repository and cloning using ssh instead of https.