// client
const socket = io(server, {
    transports: ['websocket', 'polling', 'flashsocket'],
    auth: {
        token: 'abc'
    }
});

// server
io.use((socket, next) => {
    const token = socket.handshake.auth.token;
    if (isValidJwt(token)){
        next();
    }else{
        next(new Error("Socket authentication error"));
    }
});

async function isValidJwt(token){
    jwt.verify(token, secrets.jwt, function(err, decoded) {
        if (err){
            console.log(err);
            return false;
        }else{
            //console.log(decoded);
            return true;
        }
    });
}