my $private_key = $ENV{'APPDATA'}."\\ssh_key\\putty_gen_private_key.ppk";
$sftp = Net::SFTP::Foreign->new($server, 
	                        user => $user, 
				ssh_cmd => 'plink', 
				more    => [ -i => $private_key]
				);
	$sftp->die_on_error("Unable to establish SFTP connection");