In previous versions, the Socket#id attribute was equal (or derived,
for a non-default namespace) to the underlying Engine.IO id, which is
used as a mean to authenticate the user throughout the Engine.IO
session and thus is sensitive information that should be kept secret.
The problem with reusing the Engine.IO id is that users could be
tempted to transmit this id to other clients, in order to implement
private messaging for example.
So we'll now generate a new random id for each new socket.
Please note that this id will now be different from the one found in
the query parameters of the HTTP requests.
In previous versions, a client was always connected to the default
namespace, even if it requested access to another namespace.
This meant that the middlewares registered for the default namespace
were triggered in any case, which is a surprising behavior for end
users.
This also meant that the query option of the Socket on the client-side
was not sent in the Socket.IO CONNECT packet for the default namespace:
```js
// default namespace: query sent in the query params
const socket = io({
query: {
abc: "def"
}
});
// another namespace: query sent in the query params + the CONNECT packet
const socket = io("/admin", {
query: {
abc: "def"
}
});
```
The client will now send a CONNECT packet in any case, and the query
option of the Socket is renamed to "auth", in order to make a clear
distinction with the query option of the Manager (included in the query
parameters of the HTTP requests).
```js
// server-side
io.use((socket, next) => {
// not triggered anymore
});
io.of("/admin").use((socket, next => {
// triggered
console.log(socket.handshake.query.abc); // "def"
console.log(socket.handshake.auth.abc); // "123"
});
// client-side
const socket = io("/admin", {
query: {
abc: "def"
},
auth: {
abc: "123"
}
});
```
The value stored in the adapter will now be used, instead of
duplicating it in the Socket class.
Breaking change: Socket#rooms is now a Set instead of an object
Closes https://github.com/socketio/socket.io/issues/2890
