my $targetserver = 'files.responsys.net';
my $sftp = Net::SFTP->new(
    $targetserver,
    user     => 'canneu_scp',
    ssh_args => {
        identity_files => [ '/tmp/responsys/capgemini.private' ],
        debug => 1,
    }
) or die "could not open connection to $targetserver\n";