Express Simple Auth不起作用

Question

我做了一个简单的登录api，无论我发送什么作为参数，它都无法正常工作，这是我的用户架构：

var mongoose = require('mongoose');
var userSchema = mongoose.Schema({
  username: {type: String, required: true , unique: true},
  password: {type: String, required: true}
});

module.exports = mongoose.model('User', userSchema);

这是我的代码：

router.post('/login', (req,res,next) => {
  var usern = req.body.username;
  var passw = req.body.password;
  console.log(usern + " " + passw);
  if ( !usern || !passw ) {
    return res.status(400).json({'error': 'Bad Request'});
  } else {
    User.findOne({username: req.body.username},(user , err)=> {
      if (!user) {
        return res.status(404).json({'error': 'No User Found'});
      } else if (user.password !== req.body.password ) {
        return res.status(401).json({'error': 'Auth Failed'});
      } else {
        return res.status(200).json({
          'success': 'true'
        });
      }
    });
  }
});

提前致谢！