Example of auth0 login

Login.js

import React from 'react';
import { StyleSheet, Text, View, Button, Alert } from 'react-native';
import { AuthSession } from 'expo';
import jwtDecode from 'jwt-decode';

/*
  You need to swap out the Auth0 client id and domain with
  the one from your Auth0 client.
  In your Auth0 client, you need to also add a url to your authorized redirect urls.
  For this application, I added https://auth.expo.io/@arielweinberger/auth0-example because I am
  signed in as the "community" account on Expo and the slug for this app is "auth0-example" (check out app.json).

  You can open this app in the Expo client and check your logs to find out your redirect URL.
*/
const auth0ClientId = 'YOUR-CLIENT-ID';
const auth0Domain = 'https://yourtenant.auth0.com';

/**
 * Converts an object to a query string.
 */
function toQueryString(params) {
  return '?' + Object.entries(params)
    .map(([key, value]) => `${encodeURIComponent(key)}=${encodeURIComponent(value)}`)
    .join('&');
}

const Login = () => {

  const loginFunc = async () => {
    // Retrieve the redirect URL, add this to the callback URL list
    // of your Auth0 application.
    const redirectUrl = AuthSession.getRedirectUrl();
    console.log(`Redirect URL: ${redirectUrl}`); // <-- you will need to set this in your allowed urls in auth0
    
    // Structure the auth parameters and URL
    const queryParams = toQueryString({
      client_id: auth0ClientId,
      redirect_uri: redirectUrl,
      response_type: 'id_token', // id_token will return a JWT token
      scope: 'openid profile', // retrieve the user's profile
      nonce: 'nonce', // ideally, this will be a random value
    });
    const authUrl = `${auth0Domain}/authorize` + queryParams;
    // Perform the authentication
    const response = await AuthSession.startAsync({ authUrl });
    console.log('Authentication response', response);
  };
}