User.findOne({where: {username: req.body.username}}).then(user => {
  if (!user) {
    User.create({username: req.body.username, password: bcrypt.hashSync(req.body.password)})
        .then(() => res.status(201).send({message: "Created user."}))
        .catch(err => next(err));
    } else {
      res.status(400).send({message: "Username already exists."});
    }
});