React SPA OAuth Login

auth.js

module.exports = {
  login (email, pass, cb) {
    cb = arguments[arguments.length - 1]
    if (localStorage.token) {
      if (cb) cb(true)
      this.onChange(true)
      return
    }
    fetch('http://localhost:5000/api/oauth2/token', {
      method: 'POST',
      headers: {
        'Accept': 'application/json',
        'Content-Type': 'application/json',
      },
      body: JSON.stringify({
        username: email,
        password: pass,
        grant_type: 'password',
        client_id: 'imp_local_id',
        client_secret: 'imp_local_secret'
      })
    }).then(res => res.json())
      .then(res => {
        localStorage.token = res.access_token.token
        if (cb) cb(true)
        this.onChange(true)
      })
      .catch(e => {
        if (cb) cb(false)
        this.onChange(false)
      })
  },
  logout (cb) {
    fetch('http://localhost:5000/logout')
      .then((res) => {
        delete localStorage.token
        if (cb) cb()
        this.onChange(false)
      }).catch(e => {
        console.log(e)
      })
  },
  getToken () {
    return localStorage.token
  },
  loggedIn () {
    return !!localStorage.token
  },
  onChange () {}
}

Login.react.js

import React, { Component } from 'react';
import {withRouter} from 'react-router';
import auth from '../auth';

class Login extends Component {
  constructor() {
    super()
    this.state ={
      error: true
    };
    this.handleSubmit = this.handleSubmit.bind(this);
  }

  handleSubmit(event) {
    event.preventDefault();
    const email = this.refs.username.value;
    const pass = this.refs.password.value;

    auth.login(email, pass, (loggedIn) => {
      if (!loggedIn)
        return this.setState({ error: true });

      const { location } = this.props;

      if (location.state && location.state.nextPathname) {
        this.props.router.replace(location.state.nextPathname);
      } else {
        this.props.router.replace('/dashboard');
      }
    })
  }

  render() {
    return (
      <div className="container">
        <form onSubmit={this.handleSubmit} style={{maxWidth: '350px', margin: '2rem auto' }}>
          <input type="text" ref="username" defaultValue="jared" placeholder="username"/>
          <input type="password" ref="password" placeholder="password" />
          <input type="submit" value="Login"/>
          {this.state.error && (
           <p>Bad login information</p>
         )}
        </form>
      </div>
    );
  }
}

export default withRouter(Login);