Fastify

chanxFastify from @chanx-js/server/fastify registers a route per consumer path, through @fastify/websocket:

npm install @chanx-js/server @fastify/websocket

import Fastify from 'fastify';
import websocket from '@fastify/websocket';
import { chanxFastify } from '@chanx-js/server/fastify';

import { chanx } from './app.js';

const app = Fastify();
await app.register(websocket);
await app.register(chanxFastify(chanx));

app.get('/asyncapi.json', () => chanx.asyncapi());

await app.listen({ port: 8000 });

• Register @fastify/websocket first; chanxFastify throws if it is missing.
• Register it without a prefix: the routes are the consumers' own paths.
• chanxFastify(chanx, { pingInterval, maxBufferedAmount }) takes the same options as the Node adapter, with the same defaults.
• @fastify/websocket closes the sockets when Fastify closes; its preClose option sets how.

Refusing an upgrade in a hook

Fastify's hooks run before each upgrade, so an onRequest hook or an auth plugin can refuse one with an HTTP status, which a client sees before any socket opens:

app.addHook('onRequest', async (request, reply) => {
  if (request.url.startsWith('/ws/admin') && !isAdmin(request)) {
    await reply.code(403).send({ detail: 'Admins only' });
  }
});

For refusals that belong to the consumer, use its own authenticate, which works the same on every adapter.