code: func (c *Client) CreateSession(sess session.Session) error {
  	if sess.Namespace == "" {
  		return trace.BadParameter(MissingNamespaceError)
  	}
  	_, err := c.PostJSON(c.Endpoint("namespaces", sess.Namespace, "sessions"), createSessionReq{Session: sess})
  	return trace.Wrap(err)
  }
docs: // CreateSession creates new session