userservice.js

var userService = mongodb({
  db: 'feathers-demo',
  collection: 'users'
}).extend({
  authenticate: function(username, password, callback) {
    // This will be used as the MongoDB query
    var query = {
      username: username
    };

    this.find({ query: query }, function(error, users) {
      if(error) {
        return callback(error);
      }

      var user = users[0];

      if(!user) {
        return callback(new Error('No user found'));
      }

      // Compare the hashed and salted passwords
      if(user.password !== hash(password, user.salt)) {
        return callback(new Error('User password does not match'));
      }

      // If we got to here, we call the callback with the user information
      return callback(null, user);
    });
  }
});

app.configure(feathers.socketio(function(io) {
  io.on('connection', function(socket){
    io.on('login', function(username, password, callback) {
      app.service('users').authenticate(username, password, function(error, user) {
        socket.feathers.user = user;
        callback(error, user);
      });
    });
  });
}).use(userService);