Your welcome, I'm learning a lot from interesting questions.

The code is mostly adopted from the perldoc though and could be written in a more generic way.

I also like the fact that JSON::PP automatically detects hashes ordered via tie interface.

> I knew that JSON used JSON::PP or JSON::XS under the hood,

Not only under the hood, you can even use both modules in the same code, as long as you are restricting one of them to pure OO. =)

use warnings;
use strict;
use autodie;

use JSON::PP qw//;                      # don't export anything
use JSON;

use Test::More;

use 5.010;

my @order = qw/id disp ver auth/;



my $dat = [ ({ id => 'a', disp => 'a', ver => 'a', auth => 'a' })x2 ];
+ # dummy data

local $\ = "\n";

#print 'Unsorted => ', JSON->new->indent->space_after->encode( $dat );
#print 'Alpha Sorted => ', JSON->new->indent->space_after->canonical->
+encode( $dat );
print "Pryrt's Order => ",
    my $pryrt = manual_ordered_json( $dat, \@order );

# --- Sorting with JSON::PP
my %ORDER;
@ORDER{@order} = 1 .. @order;
my $sort = sub {
    package JSON::PP;
    ($ORDER{$a} // 1e999) <=> ($ORDER{$b} // 1e999)
        or
    $a cmp $b
    };
print "LanX' Order => ",
    my $lanx = JSON::PP->new->sort_by($sort)->indent->space_after->enc
+ode( $dat );

# # --- erase whitespace diffs
# s/\s//g for $pryrt, $lanx;

is($lanx,$pryrt,"same JSON");

done_testing();

use Data::Dumper;

sub manual_ordered_json{
    my @list = @{$_[0]};
    my @ordr = @{$_[1]};
    my $out = "[\n";
    for my $i ( 0 .. $#list ) {
        my $h = $list[$i];
        $out .= "   {\n";
        for my $j ( 0 .. $#ordr ) {
            my $k = $ordr[$j];
            next unless defined $k;
            next unless exists $h->{$k};
            $out .= sprintf qq|      "%s": "%s"|, $k, $h->{$k} // '<un
+def>';
            $out .= ',' if $j < $#ordr;
            $out .= "\n";
        }
        $out .= "   }";
        $out .= "," if $i < $#list;
        $out .= "\n";
    }
    $out .= "]\n";
    return $out;
}
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