client.js

var faye = require('faye'),
    sys  = require('sys');

var client = new faye.Client('http://127.0.0.1:8000/faye');

client.subscribe('/messages', function(message) {
  // This should never run due to server-side extension
  sys.puts(sys.inspect(message));
});

setInterval(function() {
  client.publish('/messages', {hello: 'world'});
}, 1000);

server.js

var http = require('http'),
    sys  = require('sys'),
    faye = require('faye');

var serverProtection = {
  incoming: function(message, callback) {
    if (message.channel !== '/meta/subscribe' || message.subscription !== '/messages')
      return callback(message);
    
    if (!message.ext || message.ext.authToken !== 'whatever')
      message.error = 'I need an authToken!';
    
    callback(message);
  }
};

var clientAuthentication = {
  outgoing: function(message, callback) {
    if (message.channel !== '/meta/subscribe' || message.subscription !== '/messages')
      return callback(message);
    
    message.ext = message.ext || {};
    message.ext.authToken = 'whatever';
    
    callback(message);
  }
};

var server = http.createServer(),
    bayeux = new faye.NodeAdapter({mount: '/faye', timeout: 45});

bayeux.addExtension(serverProtection);

bayeux.attach(server);
server.listen(8000);

var client = bayeux.getClient();
client.addExtension(clientAuthentication);

client.subscribe('/messages', function(message) {
  sys.puts(sys.inspect(message));
});