Chat Application using Spring boot RSocket

Question

I am using Spring boot 2.5.0 with the react front end. Trying to use RSocket for building a chat application.

Came across the following links. But, still not clear on sending message to a particular user.

RSocket doc --> https://docs.spring.io/spring-framework/docs/5.3.8-SNAPSHOT/reference/pdf/rsocket.pdf

Medium --> https://medium.com/swlh/building-a-chat-application-with-angular-and-spring-rsocket-3cd8013f2f55

RSocket Demo -> https://github.com/benwilcock/spring-rsocket-demo/blob/master/rsocket-server/src/main/java/io/pivotal/rsocketserver/RSocketController.java

My application is a multi tenant application. Each tenant might have 3 to 10 users.

Use cases, For any given tenant,

1. Store messages in the server
2. Should be able to list the users online
3. Send message to all users belongs to a particular tenant
4. Send message to a particular user from a tenant

I have the following config.

In build.gradle,

implementation 'org.springframework.boot:spring-boot-starter-rsocket'

application.properties,

spring.rsocket.server.mapping-path= /rsocket
spring.rsocket.server.transport= websocket

RSocketController.java

@MessageMapping("fire-and-forget")
    public Mono<Void> fireAndForget(final Message request, @AuthenticationPrincipal UserDetails user) {
        return Mono.empty();
    }

Here, I am able to get the user message and need to route this to a particular user/users. How can I find all users online and route message to a particular user/users?