If you're using CGI.pm and you have it generate the forms, a real easy hack is to override the different forms subs to include them automatically for you.

######################################
sub persistant_fields {
    my @fields = qw(username  sessionID);

    my $text = undef;

    foreach (@fields){
        $text.=input ({-name=>$_, -type=>'HIDDEN', -value=>param($_) }
+ )."\n" if param($_);
    }
    
    return $text;


}
######################################
sub form_ID{
         input ({-name=>'formID', -type=>'HIDDEN', -value=>substr(md5_
+hex(time.$$.rand()), 0, 32) } )
}
######################################
sub start_form {
    CGI::start_form(@_).form_ID().persistant_fields();
}
######################################
sub start_multipart_form {
    CGI::start_multipart_form(@_).form_ID().persistant_fields();
}
[download]