[RFE] Multiple ssh-agent support

[Philipp Marek]

> > unlinking the socket seems a bit overkill. You could play with
> > SSH_AUTH_SOCK
> 
> Playing with SSH_AUTH_SOCK may be a bit problematic. As far as I
> understand it would require a session restart in order to set a new
> value to the env var (at least using GNOME).
> Btw, I would like to be really clear here that I am focused in a
> DE-agnostic solution. :-)
Well, just move the existing socket aside (to another name in the same 
directory), and have your spice agent provide a socket with the original 
name.

> > I would make a proxy ssh agent that linearly attempts from each
> > child agent. The add operations would always go to the first agent
> > (unless it returned an error?).
That sounds easy enough - after moving the "original" socket aside, fall 
back to queries on that one if the "new" agent can't answer.

That way we'd get a chain of agents, each asking the "older"/previous if 
needed.

> > I also like the idea of SSH_AUTH_SOCK containing a list of sockets.
Uh, that sounds like more complexity - and that means more code.
As the ssh-agent is handling private keys, it should be as small as 
possible - forwarding queries to only one (the next one) is enough for
this use case.


> The proxy agent would be the spice one or the one already running in the system?
I guess that the spice-agent wouldn't add keys back to the developer 
machine; that runs a bit against having the key on the VM (and only the 
VM), if it routinely gets moved across the network.

So I guess the spice agent would need to provide it, by storing it in the 
VM system agent.