Here's how I do it:

use strict;
use LWP::UserAgent;

my $url = 'http://foobar.com';
my %postdata = (key => 'value', key2 => 'value2');

my $ua = LWP::UserAgent->new;
my $response = $ua->post($authorize_url,[%postdata]);

if ($response->is_success) {
  print $response->content;
} else {
  print "Post Failed!\n";
}
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