How to make private messages on Yii2 & Socket.io?

Question

Yii

Hello!
1. There is a modular Yii2-basic application with cookie-based authorization borrowed from the advanced template. It has a message module.
2. Added another Node(express, socket.io, redis) server.
3. When a user sends a message, information about it is also sent to the Redis channel.
4. Socket.io is subscribed to this channel, but does not know to whom to send, to which room (for example, user_id).
How to implement message delivery to a specific user via socket.io? How to identify a user in Node?