bare-bones generate temporary access URL to non-public Amazon S3 resource

geturl.php

<?php

$key = 'SECRET_ACCESS_KEY_ID';
$accesskeyid='ACCESS_KEY_ID';

$expires = time()+60; // URL expires in 60 seconds
$stringtosign = "GET\n\n\n{$expires}\n/BUCKET_NAME/PATH/TO/RESOURCE.EXT";

$signature = urlencode(base64_encode(hash_hmac('sha1',$stringtosign,$key,true)));

echo 'https://BUCKET_NAME.s3.amazonaws.com/PATH/TO/RESOURCE.EXT?'
      .'AWSAccessKeyId='.$accesskeyid
      .'&Signature='.$signature
      .'&Expires='.$expires;