- hash_hmac: documentation ( source)
- base64_encode: documentation ( source)
<?php
$input = 'POST
3f21fae774c49992948753328f3ab4da
Wed, 18 Jun 2014 10:05:28 GMT';
$key = '1UBD5+waM7ghc8lPTX/JsCAK/OAvtfQyi/23JvWGhNqZC+BMsWW0y6WkJ8fj2yuRigIIInm5NxSv80OxunYm9toGiJRzy+5I8EGWisMAmELnChh61YGCHMuXu6834ouD';
$hmac = hash_hmac('sha512', $input, $key, true); // true voor binary output
echo base64_encode($hmac);