module.exports = exports = function(req, res, next) {
  User.find({ username: req.body.username }, (err, user) => {
    if (err) return handleDBError(err, res);
    if (user) return res.status(200).json({ msg: 'an account with this username already exists' });
  });
  next();
};

var userSchema = new mongoose.Schema({
  username: String,
  authentication: {
    email: String,
    password: String
  }
});