meteor-accounts-passport-step1.js

function deserializeUserPassport(id, done) {
  User.findOne({ _id: id }, (err, userModel) => {
    if (err) {
      done(err);
    } else {
      if (!userModel) {
        done();
        return;
      }
      done(null, userModel.toJSON());
    }
  });
}

// let's use User id
passport.serializeUser((user, done) => done(null, user._id));
passport.deserializeUser(deserializeUserPassport);