SSH_AUTH_SOCK environment variable not available to Rex

Describe the bug

I ran into a bug where SSH ForwardAgent was enabled for a server, and I could run from the command-line

ssh -A server "cd /dir && git pull origin main"

but when running that git command in Rex (including using the SCM checkout function) did not work, and received a "Permission denied (public key)" error. See https://groups.google.com/g/rex-users/c/5FavxuXgeb0

The problem was caused by the .ssh/config having a Hostname parameter for the server that specified the IP address. Removing the Hostname fixed the issue.

Upon further investigation, I created a Rex task

task "PrintEnv" => sub {
     my $out = run "printenv";
     say $out if $out;
}

and compared using rex -H server PrintEnv with ssh -A server printenv

A notable difference is that the SSH_AUTH_SOCK environment variable was not set when run through Rex.

When removing the Hostname and re-running the Rex task, SSH_AUTH_SOCK was present. (This seems to have nothing to do with the .ssh/known_hosts although removing it the first time prompts SSH to accept the host fingerprint.)

Expected behavior

Git and other tools being run through Rex would have had their authentication forwarded.

How to reproduce it

For a .ssh/config of a particular server

1. Include a Hostname with the IP address of the server
2. Ensure ForwardAgent is "yes" for the server
3. Run a Rex command on the server that requires forwarded authentication, e.g. git pull

Code example

No response

Additional context

No response

Rex version

1.14.3

Perl version

5.34.0

Operating system running rex

Linux (Ubuntu 22.04.1)

Operating system managed by rex

Linux (Ubuntu 18.04.6, Debian 6.1.85-1)

How rex was installed?

cpan client

Start by reproducing the issue with an SSH config entry that sets Hostname to the server IP and ForwardAgent to yes, then compare rex -H server PrintEnv with ssh -A server printenv. Trace Rex's SSH connection and remote environment handling; done means SSH_AUTH_SOCK is available through Rex and a remote git pull succeeds with forwarded authentication.