def default_params
      default_params = {
        'Format'           => 'JSON',
        'SignatureMethod'  => 'HMAC-SHA1',
        'SignatureNonce'   => SecureRandom.hex(16),
        'SignatureVersion' => '1.0',
        'Timestamp'        => Time.now.utc.strftime('%Y-%m-%dT%H:%M:%SZ'),
        'AccessKeyId'      => self.access_key_id,
        'Version'          => self.api_version,
      }
      default_params.merge!('SecurityToken' => self.security_token) if self.security_token

##</code><code>##

$req->header('Content-Type' => 'application/json; charset=UTF-8');