Amazon Signature Ruby

amazon_signature.rb

module AmazonSignature
  extend self

  def signature
    Base64.encode64(
        OpenSSL::HMAC.digest(
          OpenSSL::Digest.new('sha1'),
          AWS_CONFIG['secret_access_key'], self.policy
        )
      ).gsub("\n", "")
  end

  def policy
    Base64.encode64(self.policy_data.to_json).gsub("\n", "")
  end

  def policy_data
    {
      expiration: 10.hours.from_now.utc.iso8601,
      conditions: [
        ["starts-with", "$key", AWS_CONFIG['key_start']],
        ["starts-with", "$x-requested-with", "xhr"],
        ["content-length-range", 0, 20.megabytes],
        ["starts-with", "$content-type", ""],
        {bucket: AWS_CONFIG['bucket']},
        {acl: AWS_CONFIG['acl']},
        {success_action_status: "201"}
      ]
    }
  end

  def data_hash
    {
      :bucket => AWS_CONFIG['bucket'],
      :region => AWS_CONFIG['region'], 
      :keyStart => AWS_CONFIG['key_start'],
      :params => {
        :acl => AWS_CONFIG['acl'],
        :AWSAccessKeyId => ENV['access_key_id'],
        :signature => self.signature,
        :policy => self.policy
      }
    }
  end
end

AWS_CONFIG.rb

AWS_CONFIG = {
  'access_key_id' => YOUR_ACCESS_KEY,
  'secret_access_key' => YOUR_SECRET_ACCESS_KEY,
  'bucket' => 'froala',
  'acl' => 'public-read',
  'key_start' => 'uploads/',
  'region' => 's3' # For other regions than us-east-1, use s3-region. E.g.: s3-eu-west-1
}

CORS file

<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
    <CORSRule>
        <AllowedOrigin>REPLACE_THIS_WITH_THE_URL_OF_THE_PAGE_WHERE_YOU_USE_THE_EDITOR</AllowedOrigin>
        <AllowedMethod>GET</AllowedMethod>
        <AllowedMethod>POST</AllowedMethod>
        <AllowedMethod>PUT</AllowedMethod>
        <MaxAgeSeconds>3000</MaxAgeSeconds>
        <AllowedHeader>*</AllowedHeader>
    </CORSRule>
</CORSConfiguration>

How to fix the "preflight request" error -

Change:

region: 's3', // Change the region if it is different

To your region, which for me was:

region: 's3-us-west-2', // Change the region if it is different

To find the correct region, since I tried just "us-west-2" which didn't work, I had to look at URL for a previously uploaded image in that bucket, where I found the full region name; "s3-us-west-2"

Hope that helps!