node.js, socket.io with SSL

Use a secure URL for your initial connection, i.e. instead of "http://" use "https://". If the WebSocket transport is chosen, then Socket.IO should automatically use "wss://" (SSL) for the WebSocket connection too.

Update:

You can also try creating the connection using the 'secure' option:

var socket = io.connect('https://localhost', {secure: true});

The following is how I set up to set it up with express:

    var app = require('express')();
    var https = require('https');
    var fs = require( 'fs' );
    var io = require('socket.io')(server);

    var options = {
        key: fs.readFileSync('./test_key.key'),
        cert: fs.readFileSync('./test_cert.crt'),
        ca: fs.readFileSync('./test_ca.crt'),

        requestCert: false,
        rejectUnauthorized: false
    }

    var server = https.createServer(options, app);
    server.listen(8080);
    

    
    io.sockets.on('connection', function (socket) {
        // code goes here...
    });
    
    app.get("/", function(request, response){
        // code goes here...
    })
   

Update : for those using lets encrypt use this

var server = https.createServer({ 
                key: fs.readFileSync('privkey.pem'),
                cert: fs.readFileSync('fullchain.pem') 
             }, app);

On the same note, if your server supports both http and https you can connect using:

var socket = io.connect('//localhost');

to auto detect the browser scheme and connect using http/https accordingly. when in https, the transport will be secured by default, as connecting using

var socket = io.connect('https://localhost');

will use secure web sockets - wss:// (the {secure: true} is redundant).

for more information on how to serve both http and https easily using the same node server check out this answer.