redactor_s3.php

<?php
$aws_key = '<key>';
$s3_secret = '<secret>';
$bucket_name = '<bucket>';

// Duration before request expires
$duration = (60 * 5); // 5 minutes

$objectName = $_GET['name'];

$mimeType = $_GET['type'];
$expires = time() + $duration;
$amzHeaders = "x-amz-acl:public-read";

$stringToSign = "PUT\n\n" . $mimeType . "\n" . $expires . "\n" . $amzHeaders . "\n" . "/". $bucket_name ."/" . $objectName;
$signature = urlencode(base64_encode(hash_hmac('sha1', $stringToSign, $s3_secret, true)));

$url = urlencode('https://'. $bucket_name .'.s3.amazonaws.com/' . $objectName . '?AWSAccessKeyId=' . $aws_key . '&Expires=' . $expires . '&Signature=' . $signature);

echo $url;