Amazon S3 POST api, and signing a policy with NodeJS

Question

I\'m trying to get an built that allows users to upload a file directly to my Amazon S3 bucket, from a NodeJS powered website. It seems the only tutorials out there, other t

Answer 1

I modified a bit previous example, because it didn't work for me: amazon returned an error about broken signature.

Here is how the signature should be created for Browser-Based Uploads Using POST (AWS Signature Version 4)

http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-authentication-HTTPPOST.html

var CryptoJS = require("crypto-js");

var accessKeyID = "PUT YOUR DATA";
var secretAccessKey = "PUT YOUR DATA";

var bucket = "PUT YOUR BUCKET NAME";
var region = "eu-central-1"; // overwrite with your region
var folder = "users/"; // overwrite with your folder
var expiration = "2015-09-28T12:00:00.000Z"; // overwrite date
var date = "20150927"; // overwrite date
var serviceName = "s3";


function getSignatureKey(key, dateStamp, regionName, serviceName) {
   var kDate = CryptoJS.HmacSHA256(dateStamp, "AWS4" + key);
   var kRegion = CryptoJS.HmacSHA256(regionName, kDate);
   var kService = CryptoJS.HmacSHA256(serviceName, kRegion);
   var kSigning = CryptoJS.HmacSHA256("aws4_request", kService);

   return kSigning;
}

var s3Policy = {"expiration": expiration,
  "conditions": [
   {"bucket": bucket},
   ["starts-with", "$key", folder],
   {"acl": "public-read"},
   ["starts-with", "$Content-Type", "image/"],
   {"x-amz-meta-uuid": "14365123651274"},
   ["starts-with", "$x-amz-meta-tag", ""],
   {"x-amz-credential": accessKeyID + "/" + date + "/" + region + "/" + serviceName +"/aws4_request"},
   {"x-amz-algorithm": "AWS4-HMAC-SHA256"},
   {"x-amz-date": date + "T000000Z" }
  ]
};

var base64Policy = new Buffer(JSON.stringify(s3Policy), "utf-8").toString("base64");
console.log('base64Policy:', base64Policy);

var signatureKey = getSignatureKey(secretAccessKey, date, region, serviceName);
var s3Signature = CryptoJS.HmacSHA256(base64Policy, signatureKey).toString(CryptoJS.enc.Hex);
console.log('s3Signature:', s3Signature);

Next generated base64Policy and s3Signature i used in the form for uploading. Example is here: http://docs.aws.amazon.com/AmazonS3/latest/API/sigv4-post-example.html

Very important is to check that you have the same fields and values in the html form and in your policy.