code: func (c *Client) SessionAsync() FutureSessionResult {
  	// Not supported in HTTP POST mode.
  	if c.config.HTTPPostMode {
  		return newFutureError(ErrWebsocketsRequired)
  	}
  
  	cmd := btcjson.NewSessionCmd()
  	return c.sendCmd(cmd)
  }
docs: // SessionAsync returns an instance of a type that can be used to get the result
  // of the RPC at some future time by invoking the Receive function on the
  // returned instance.
  //
  // See Session for the blocking version and more details.
  //
  // NOTE: This is a btcsuite extension.