my $pty = IO::Pty->new;
my $expect = Expect->init($pty);
my $child = open2($in, $out, '-');
if (defined $child and !$child) {
    $pty->make_slave_controlling_terminal;
    exec @cmd;
    exit -1;
}
unless (defined $child) {
    die "unable to spawn new process";
}
$expect->expect($timeout, "...");
...

# and once the authentication phase is over, $in and $out are used for the rest of the IPC.