Perl & Facebook json signed_request parsing - facebook

Question

I'm trying to parse the json signed_request you receive from Facebook in perl but need a little help!
($encoded_sig, $payload) = split('\.', $formdata{'signed_request'});
$sig = decode_base64url($encoded_sig);
$data = decode_json(decode_base64url($payload));
%decoded = %{ decode_json(decode_base64url($payload)) };
$expected_sig = hmac_sha256($payload, $app_secret);
if ($expected_sig eq $sig) {
while (my ($key, $value) = each %decoded) {
print "$key = $value\n<br>";
}
}
Each $value can either contain a string or a reference to another HASH (and some of those HASHs may contain another HASH), is there a better way to process this?
The script above returns:
algorithm = HMAC-SHA256
page = HASH(0x632b100)
issued_at = 1323081670
user = HASH(0x632b150)
and the json received after decoding is:
{"algorithm":"HMAC-SHA256","issued_at":1323081670,"page":{"id":"192130540873448","liked":true,"admin":true},"user":{"country":"gb","locale":"en_GB","age":{"min":21}}}
Ideally would like to see a result of:
algorithm = HMAC-SHA256
page-id = 192130540873448
page-liked = true
page-admin = true
issued_at = 1323081670
user-country = gb
user-locale = en_GB
user-age-min = 21
Data structure will increase as upon an authorised user response from Facebook more data is provided.
Many thanks

Answer 1

Initially I posted an URL with a working example. Thanks to Brad for pointing out that it's better to provide a code here, so I removed an URL and included the code below:
#!/usr/bin/perl
use strict;
use CGI;
use MIME::Base64;
use JSON;
use Digest::SHA qw(hmac_sha256);
my $secret = '<secret>';
my $q = new CGI;
my $sreq = $q->param('signed_request');
eval {
die 'not a signed_request' unless (defined $sreq);
my ($esig, $pload) = split('\.', $sreq);
$esig = decode_base64url($esig);
my $vsig = hmac_sha256($pload, $secret);
die 'invalid signature' unless ($esig eq $vsig);
my $data = decode_json(decode_base64url($pload));
print "Content-Type: text/html\n\n";
if ($data->{'page'}->{'liked'} eq 'true') {
print "Oh yeah, you liked me :-)";
} else {
print "No? why not? Please press the Like button";
}
};
if ($#) {
print "Content-Type: text/html\n\ndied: $#";
}
sub decode_base64url {
my $s = shift;
$s =~ tr[-_][+/];
$s .= '=' while length($s) % 4;
return decode_base64($s);
}
sub parse_hash {
my $hash = shift;
my $array = [];
foreach my $key (keys %$hash) {
if (ref($hash->{$key}) eq 'HASH') {
push #$array, $key . ' => {' . join(', ', #{ parse_hash($hash->{$key}) }) . '}';
} else {
push #$array, $key . ' => ' . $hash->{$key};
}
}
return $array;
}

Answer 2

To answer my own question :)
if ($expected_sig eq $sig) {
while (my ($key, $value) = each %decoded) {
if (ref($value) eq "HASH") {
while ( my ($key2, $value2) = each(%{$value}) ) {
$mydata{"$key-$key2"}=$value2;
if (ref($value2) eq "HASH") {
while ( my ($key3, $value3) = each(%{$value2}) ) {
$mydata{"$key-$key2-$key3"}=$value3;
print "$key-$key2-$key3 = $value3\n<br>";
}}
else
{
print "$key-$key2 = $value2\n<br>";
}}}
else
{
$mydata{"$key"}=$value;
print "$key = $value\n<br>";
}}}
outputs:
algorithm = HMAC-SHA256
page-admin = 1
page-liked = 1
page-id = 192130540873448
issued_at = 1323081670
user-country = gb
user-locale = en_GB
user-age-min = 21

Answer 3

Only way is:
$my_algorithm = $algorithm
$page-id = $page->{'id'};
$page-liked = $page->{'linked'};
$page-admin = $page->{'admin'};
$my_issued_at = $issued_at
$user-country = $user->{'country'};
$user-locale = $user->{'locale'};
$user-age-min = $user->{'age'}->{'min'};