There is an open issue to implement SSH support for the package manager:
Until it is implemented, there’s no way to fetch packages that exist in private repositories accessible by git+ssh only. Unfortunately that includes all the codebases at my day job - and I imagine, many other companies who work on commercial closed-source software.
Currently I’m working around this by cloning the code repositories I need manually and then adding them to my build.zig.zon file like this:
As a workaround, you might be able to create an ssh tunnel, and expose it locally as plain unencrypted git? Not sure if possible, but maybe worth exploring.