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
    {:signature => self.signature, :policy => self.policy, :bucket => AWS_CONFIG['bucket'], :acl => AWS_CONFIG['acl'], :key_start => AWS_CONFIG['key_start'], :access_key => AWS_CONFIG['access_key_id']}
  end
end