Secure Attachment module

module SecureAttachment
  private
  def has_secure_attached_file(name, options = {})
    has_attached_file name,        
        options.reverse_merge(
        :path => "#{name}/:id/:style/:basename.:extension",
        :storage => :s3,
        :s3_credentials => "#{RAILS_ROOT}/config/s3.yml",
        :s3_protocol => 'https',
        :s3_permissions => 'private',
        :bucket => "#{BUCKET_APP_NAME}-#{Rails.env}-private")

    define_method "#{name}_time_limited_url" do |*args|
      attachment = send(name)
      options = args.last || {}
      style = options[:style]
      expire_in = options[:expire_in] || 10.minutes
      attachment.s3.interface.get_link(attachment.s3_bucket.to_s, 
                                  attachment.path(style), expire_in) 
    end
  end
end


### in your model:

class SomeModel < ActiveRecord::Base
  extend SecureAttachment

  has_secure_attached_file :attachment
end