code: func SetBasicAuth(username, password string) ClientOptionFunc {
  	return func(c *Client) error {
  		c.basicAuthUsername = username
  		c.basicAuthPassword = password
  		c.basicAuth = c.basicAuthUsername != "" || c.basicAuthPassword != ""
  		return nil
  	}
  }
docs: // SetBasicAuth can be used to specify the HTTP Basic Auth credentials to
  // use when making HTTP requests to Elasticsearch.