git2-rs (0.19.0) on Mac does not appear to support using passworded ssh keys from ssh-agent. I haven't yet tested on Linux but I'd like to make something that works on both platforms.

I tested with both RemoteConnection (with credentials callback set using Cred::ssh_key_from_agent) and Repository.find_remote(...).fetch(...) with FetchOptions credentials callback using ssh_key_from_agent. I confirmed that the callback is getting called by adding a panic which does hit when trying to connect or fetch.

Minimal repro published to https://github.com/mbanack/git2-ssh-agent-repro

Is there some other library mechanism that supports passworded keys? It appears that the git command line utilities support this by querying ssh-agent, which I assume is accomplished by the system libgit2.