use HTML::TreeBuilder;
my $tree = HTML::TreeBuilder->new;
$tree->parse($content);
$tree->eof;
my @hidden_field_elements = $tree->look_down(
    _tag => "input",
    type => "hidden",
);
my %hidden_fields = 
    map { $_->attr('name') => $_attr('value') }
        @hidden_field_elements;