SYNOPSIS
# Functional style
use Digest::HMAC_SHA1 qw(hmac_sha1 hmac_sha1_hex);
$digest = hmac_sha1($data, $key);
print hmac_sha1_hex($data, $key);
# OO style
use Digest::HMAC_SHA1;
$hmac = Digest::HMAC_SHA1->new($key);
$hmac->add($data);
$hmac->addfile(*FILE);
$digest = $hmac->digest;
$digest = $hmac->hexdigest;
$digest = $hmac->b64digest;