Amazon s3 direct upload with Cordova (Phonegap)

file_upload.js

function upload_media(imgURI) {
  var options = new FileUploadOptions();
  options.fileKey="file";
  var time = new Date().getTime();
  var fileName = time+".jpg";
  options.fileName = fileName;
  options.mimeType ="image/jpeg";
  options.chunkedMode = false;
   
  var uri = encodeURI("http://<your bucket name>.s3.amazonaws.com/");
   
  var policyDoc = '<Base 64 policy doc>';
  var signature = '<Generated Signature>';
  var params = {
    "key": "media/"+fileName,
    "AWSAccessKeyId": "<Your AWS Access Key>",
    "acl": "public-read",
    "policy": policyDoc,
    "signature": signature,
    "Content-Type": ""
  };
  options.params = params;
   
  var ft = new FileTransfer();
  ft.upload(imgURI, uri, function() {
    console.log("Success! :)");
  },
  function() {
    console.log("Failure! :(");
  }, options);
}

signature_generator.rb

require 'base64'
require 'openssl'
require 'digest/sha1'

policy_document = IO.read('policy_document')

policy = Base64.encode64(policy_document).gsub("\n","")

signature = Base64.encode64(
    OpenSSL::HMAC.digest(
        OpenSSL::Digest::Digest.new('sha1'), 
        '<Your Secret Key>', policy)
    ).gsub("\n","")

puts "Policy: #{policy}"
puts "Signature: #{signature}"