Passport.js - return partial user object

So I'm using passport.js authentication and storing several subdocuments that are relevant to my User model:

var UserSchema = new Schema({
  fullName: {
    type: String,
    trim: true,
    default: ''
  },
  actions: [{
    title: String,
    step: Number,
    addIf: [String],
    added: { type: Date, default: Date.now }
  }]
});

I'm new to passport, but curious to know how I can configure it to provide only a part of this User Model during the log in process, akin to:

User.findOne({
  _id: id
}, '-actions', function(err, user) {
  // get user object
});

Where is the best place to add this middleware?