Setup your application's code

# installation with npm
npm install --save auth0-js

# installation with yarn
yarn add auth0-js

The auth0.js library can also be retrieved from Auth0's CDN.

<script src="https://cdn.auth0.com/js/auth0/8.12.3/auth0.min.js"></script>

Add the following lines to your base code

// src/App.js

import React, { Component } from 'react';
import { Navbar, Button } from 'react-bootstrap';
import './App.css';

class App extends Component {
  goTo(route) {
    this.props.history.replace(`/${route}`)
  }

  login() {
    this.props.auth.login();
  }

  logout() {
    this.props.auth.logout();
  }

  render() {
    const { isAuthenticated } = this.props.auth;

    return (
      <div>
        <Navbar fluid>
          <Navbar.Header>
            <Navbar.Brand>
              <a href="#">Auth0 - React</a>
            </Navbar.Brand>
            <Button
              bsStyle="primary"
              className="btn-margin"
              onClick={this.goTo.bind(this, 'home')}
            >
              Home
            </Button>
            {
              !isAuthenticated() && (
                  <Button
                    bsStyle="primary"
                    className="btn-margin"
                    onClick={this.login.bind(this)}
                  >
                    Log In
                  </Button>
                )
            }
            {
              isAuthenticated() && (
                  <Button
                    bsStyle="primary"
                    className="btn-margin"
                    onClick={this.logout.bind(this)}
                  >
                    Log Out
                  </Button>
                )
            }
          </Navbar.Header>
        </Navbar>
      </div>
    );
  }
}

export default App;

Create an Application in Auth0 dashboard 

Install the Custom Social Connection extension under Extensions 

List the app under the Installed Extensions tab. Click on the Custom Social Connections

Create a twitch (oauth2) connection under Custom Social Connections

Configure your connection settings and enable your application under the Apps tab