Check the value of auth_pubtkt cookie against the public key.

check-auth-pubtkt-cookie.pl

#!/usr/bin/env perl
use strict;
use warnings;

use URI::Escape  'uri_unescape';
use MIME::Base64 'decode_base64';
use File::Temp   'tempfile';

die "usage: $0 cookie pubkey.pem\n" unless @ARGV == 2;

my ( $cookie, $pubkey ) = @ARGV;
$cookie = uri_unescape($cookie);

my ( $tkt, $sig ) = $cookie =~ m#(.*);sig=(.*)#;

$sig = decode_base64($sig);
my ( $tmpfd, $tmpfn ) = tempfile( "tktsigXXXXXX", DIR => "/tmp" );
binmode $tmpfd;
print $tmpfd $sig;
close $tmpfd;

system qq{echo -n '$tkt' | openssl dgst -sha1 -verify $pubkey -signature $tmpfn};
unlink $tmpfn;