Another option: convert the data to a JSON string base64-encoded JSON string, then sign the string.
use JSON::XS;
use Digest::MD5 'md5_hex';
use MIME::Base64;
my $signing_key = '//Sw0rdFiSh//';
my $data = {
first_name => 'Will',
last_name => 'Smith',
age => 39,
};
my $json_string = encode_json( $data );
my $signature = md5_hex( $signing_key . $json_string );
my $base64_encoded = encode_base64( $json_string, '' );
# Send the encoded data and the signature in the HTML as hidden fields
print <<"HTML";
<input type="hidden" name="_signature" value="@{[ $signature ]}" />
<input type="hidden" name="_data" value="@{[ $base64_encoded ]}" />
HTML
Later, when processing the stored data on another step:
my $json_string = decode_base64( $q->param('_data') );
my $new_signature = md5_hex( $signing_key . $json_string );
unless( $new_signature eq $q->param('_signature') )
{
die "The data has been tampered with";
}# end unless()