code: func (s *APIKeySigner) Sign(req *http.Request) error {
  	if s.KeyName == "" {
  		s.KeyName = "Authorization"
  	}
  	if s.Format == "" {
  		s.Format = "Bearer %s"
  	}
  	name := s.KeyName
  	format := s.Format
  	val := fmt.Sprintf(format, s.KeyValue)
  	if s.SignQuery && val != "" {
  		query := req.URL.Query()
  		query.Set(name, val)
  		req.URL.RawQuery = query.Encode()
  	} else {
  		req.Header.Set(name, val)
  	}
  	return nil
  }
docs: // Sign adds the API key header to the request.