code: def make_header(url,
                  access_key=None,
                  secret_key=None):
      ''' create request header function
      :param url: URL for the new :class:`Request` object.
      '''
      nonce = nounce()
      url    = url
      message = nonce + url
      signature = hmac.new(secret_key.encode('utf-8'), message.encode('utf-8'), hashlib.sha256).hexdigest()
      headers = {
         'ACCESS-KEY'      : access_key,
         'ACCESS-NONCE'    : nonce,
         'ACCESS-SIGNATURE': signature
      }
      return headerf make_header(url,
                  access_key=None,
                  secret_key=None):
      ''' create request header function
      :param url: URL for the new :class:`Request` object.
      '''
      nonce = nounce()
      url    = url
      message = nonce + url
      signature = hmac.new(secret_key.encode('utf-8'), message.encode('utf-8'), hashlib.sha256).hexdigest()
      headers = {
         'ACCESS-KEY'      : access_key,
         'ACCESS-NONCE'    : nonce,
         'ACCESS-SIGNATURE': signature
      }
      return headers
docs: create request header function
      :param url: URL for the new :class:`Request` object.