def temporary_url(expires_at = Time.now + 3600)
      signature = Signature.generate_temporary_url_signature(:bucket => name,
                                                             :resource => key,
                                                             :expires_at => expires_at,
                                                             :secret_access_key => secret_access_key)

      "#{url}?AWSAccessKeyId=#{self.bucket.service.access_key_id}&Expires=#{expires_at.to_i.to_s}&Signature=#{signature}"
    end
def temporary_url(expires_at = Time.now + 3600)
      signature = Signature.generate_temporary_url_signature(:bucket => name,
                                                             :resource => key,
                                                             :expires_at => expires_at,
                                                             :secret_access_key => secret_access_key)

      "#{url}?AWSAccessKeyId=#{self.bucket.service.access_key_id}&Expires=#{expires_at.to_i.to_s}&Signature=#{signature}"
    end
Returns a temporary url to the object that expires on the
 timestamp given. Defaults to one hour expire time.