my $owned_sites = qr/mysite\.(com|net|org)/i;

sub add_sessions {
    my $root = HTML::TreeBuilder->new_from_content( shift() );
    my $session = shift;

    foreach my $link ($root->look_down( '_tag', 'a' ) ) {
        next unless my $url = $link->attr('href');

        if ( $url =~ m|://([^/]*)/| ) {
            next if ( $1 !~ $owned_sites );
        }
        
        # Look for mailto: links.
        next if ( $url =~ m|^[^/]*:| );

        my ( $path, $params ) = split /\?/, $url, 2;
        my %params = map { split( /=/, $_, 2 ) } split( /&/, $params );
        $params{session} ||= $session;

        $url = join( '?', $path, join( '&', map { "$_=$params{$_}" } keys( %params ) ) );
        $link->attr('href', $url);
    }

    my $html = $root->as_HTML;
    $root->delete();

    return $html;
}