Google spreadsheet function for signing S3 URLs (very handy for CSV cost allocation reports when combined with the ImportData() function)

sign_s3.gs

function sign_s3(access_key, private_key, bucket, object_name, validity, base_url) {
  if(!base_url) {
    base_url = "http://s3.amazonaws.com";
  }
  if(!validity) {
    validity = 60;
  }
  expires = Math.floor((new Date()).getTime() / 1000) + validity;
  object_name = encodeURIComponent(object_name);
  stringToSign = "GET\n\n\n"+expires+"\n/"+bucket+"/"+object_name;
  signature = encodeURIComponent(Utilities.base64Encode(Utilities.computeHmacSignature(Utilities.MacAlgorithm.HMAC_SHA_1, stringToSign, private_key)));
  url = base_url+"/"+bucket+"/"+object_name+"?AWSAccessKeyId="+access_key+"&Expires="+expires+"&Signature="+signature;
  return url;
}