登录 React + Express + mongoDB 无法正常工作

我在我的项目中有一个登录认证问题。我连接了我的反应前端与我的express后端，但是当我尝试用有效的凭据登录时，它会陷入一个错误，似乎无法正确读取我在表单输入中传递的值。

这是我的登录页面:

import React, { Component } from 'react';
import { Link } from 'react-router-dom';
import PropTypes from 'prop-types';
import { connect } from 'react-redux';
import { signin } from '../actions/authAction';
import { clearErrors } from '../actions/errAction';
import { Button, Form, FormGroup, Input, Alert } from 'reactstrap'
import TopCont from '../components/TopCont'
class Signin extends Component {
state = {
email: '',
password: '',
msg: null
};
static propTypes = {
isAuth: PropTypes.bool,
signin: PropTypes.func.isRequired,
err: PropTypes.object.isRequired,
clearErrors: PropTypes.object.isRequired
};
componentDidMount(){
this.props.clearErrors();
}
componentDidUpdate(prevProps){
const { err } = this.props;
if(err !== prevProps.err) {
if(err.id === 'LOGIN_FAIL'){
this.setState({ msg: err.msg.msg });
} else {
this.setState({ msg: null });
}
}
};
onChange = e => {
this.setState({ 
[e.target.email]: e.target.value,
[e.target.password]: e.target.value
});
};
onSubmit = e => {
e.preventDefault();
const { email, password } = this.state;
const user = {
email,
password
};

this.props.signin(user);
/* this.props.push('/dashboard'); */
};
render() {
return (
<>
<TopCont>
<div className="signin-cont">
<h1>Accedi</h1>
{this.state.msg ? <Alert color="danger">{this.state.msg}</Alert> : null }
<Form className="signin-form-cont" onSubmit={this.onSubmit}>
<FormGroup>
<Input className="signin-form" type="email" name="email" id="email" placeholder="mario.rossi@prova.it" onChange={this.onChange}/>
</FormGroup>
<FormGroup>
<Input className="signin-form" type="password" name="password" id="password" placeholder="Password" onChange={this.onChange}/>
</FormGroup>
<Button className="sign-btn">Accedi</Button>
</Form>
<p>Non hai ancora un account? <Link to="/signup">Registrati</Link></p>                  
</div>
</TopCont>
</>
)
}
}
const mapStateToProps = state => ({
isAuth: state.auth.isAuth,
err: state.err
});
export default connect(mapStateToProps, { signin, clearErrors })(Signin);
这是我的动作:

import axios from 'axios';
import { returnErrors } from './errAction';
import  { AUTH_ERROR, LOGIN_FAIL } from '../actions/types';
export const signin = ({ email, password }) => dispatch => {
const  config = {
headers: {
'Content-Type': 'application/json'
}
};
const body = JSON.stringify({ email, password });
axios.post('/api/auth', body, config)
.then(res => dispatch({
type: LOGIN_SUCCESS,
payload: res.data
}))
.catch(err => {
dispatch(returnErrors(err.response.data, err.response.status, 'LOGIN_FAIL'));
dispatch({
type: LOGIN_FAIL
});
});
};
这是我的Auth API:

const express = require('express');
const router = express.Router();
const bcrypt = require('bcryptjs');
const config = require('config');
const jwt = require('jsonwebtoken');
const auth = require('../../middleware/auth');
const User = require('../../models/User');
//@action POST api/auth
//@descr auth user
//@access Public
router.post('/', (req, res) => {
const { email, password } = req.body
if( !email || !password ) {
return res.status(400).json({ msg: "Enter all fields."});
}
User.findOne({ email })
.then(user => {
if(!user) return res.status(400).json({ msg: "Nessun profilo trovato con questa email"});
bcrypt.compare( password, user.password )
.then(isMatch => {
if(!isMatch) return res.status(400).json({ msg: "Password errata!"});
jwt.sign(
{ id: user.id },
config.get('jwtSecret'),
{ expiresIn: 10800 }, 
(err, token) => {
if(err) throw err;
res.json({
token,
user: {
id: user.id,
name: user.name,
surname: user.surname,
email: user.email,
userPlus: user.userPlus
}
})
}
)
})
})
});
//@action GET api/auth/user
//@descr GET user data
//@access Private
router.get('/user', auth, (req, res) => {
User.findById(req.user.id)
.select('-password')
.then(user => res.json(user));
});
module.exports = router;
如果我试图摆脱所有的错误控制我的服务器返回这个错误:TypeError: Cannot read property 'password' of null
奇怪的是，如果我尝试注册一个新用户(使用几乎相同的组件和服务器端方法)没有问题，它验证也没有问题。
有人知道我怎么能解决这个问题?

onChange = e => {
this.setState({ 
[e.target.email]: e.target.value,
[e.target.password]: e.target.value
});
};

onChange = e => this.setState(prevState => ({
...prevState, 
[e.target.name]: e.target.value,
}));