PowerShell/Win32-OpenSSH#1263
Issue: ssh-agent is using default sign algorithm, without considering related flags in request
Fix: parse flags and consider sign algorithm input
PowerShell/Win32-OpenSSH#1234
Issue: ssh-agent has old logic to lookup sshd account
Fix: remove this redundant logic
client now connect to ssh-agent at Identification level, preventing rogue processes hosting "ssh-agent" pipes from impersonating and elevating to client context.
Since ssh-agent now cannot do ImpersonateNamedpipeClient, retrieve the client impersonation token explicitly and rely on ImpersonateLoggedonUser instead.
