GET a non-public JavaScript file from AWS S3 using their API

Question

I am attempting to follow the AWS API for getting a JavaScript file from a private S3 bucket. The guide is here: Signing and Authenticating REST Requests

The environment is a browser with jQuery, so this is a JavaScript implementation. I have worked through what I considered to be the hard part - signing the request with the secret key. But now I am hung up on something supposedly easy. I have this resulting REST request to transmit:

GET /gss3/sayHello.js HTTP/1.1
Host: gss3.s3.amazonaws.com
Date: Thu Feb 07 2013 08:16:25 GMT-0500 (Eastern Standard Time)
Authorization: AWS AKIAJTURNBE6SXNTVVGQ:eWJOLZnj6Eja3CEC2CyifeURnxg=

Since this is a call to s3.amazonaws.com from www.mydomain.com, I was looking at JSONP to get around the same origin policy. However, I don't see any way to add extra headers to a jQuery JSONP call, and to authenticate with AWS you have to pass that 4th line:

Authorization: AWS AKIAJTURNBE6SXNTVVGQ:eWJOLZnj6Eja3CEC2CyifeURnxg=

So my question is this: how the heck do I transmit this REST request to AWS in my browser / jQuery environment? What am I missing here? Thanks gang....

Answer 1

Although this source was written for PHP, the blog Amazon AWS S3 Query String Authentication with PHP shows how to compile a plain old querystring and pass the signature as a parameter to S3.

$url .= '?AWSAccessKeyId='.$awsKeyId
.'&Expires='.$expires
.'&Signature='.$signature;

Using the crypto-js and converting to Javascript then gives us something like this:

var filePath = "/bucket/file.js";
var dateTime = Math.floor(new Date().getTime() / 1000) + 300; // allows for 5 minutes clock diff
var stringToSign = "GET\n\n\n" + dateTime + "\n" + filePath;
var signature = CryptoJS.enc.Base64.stringify(CryptoJS.HmacSHA1(stringToSign, secretAccessKey));
var queryString = "?AWSAccessKeyId=" + accessKeyId + "&Expires=" + dateTime + "&Signature=" + encodeURIComponent(signature);

var script = document.createElement("script");
script.type = "text/javascript";
script.src = "https://s3.amazonaws.com/bucket/file.js" + queryString;
$("head").append(script); // jQuery version

And there you go, almost the whole banana written for you. I hope this helps someone out.