demo-auth-flow/demo-client-app/src/index.js

import React from 'react';
import ReactDOM from 'react-dom';
import './index.css';
import App from './App';
import reportWebVitals from './reportWebVitals';

import Keycloak from "keycloak-js";

const initOptions = {
  url: 'http://localhost:8080/auth', realm: 'demorealm', clientId: 'react-app', onLoad: 'login-required'
}

const keycloak = Keycloak(initOptions);

keycloak.init({ onLoad: initOptions.onLoad }).then((auth) => {
  if (!auth) {
    window.location.reload();
  } else {
    ReactDOM.render(
      <React.StrictMode>
        <App keycloak={keycloak}/>
      </React.StrictMode>,
      document.getElementById('root')
    );
    
    // If you want to start measuring performance in your app, pass a function
    // to log results (for example: reportWebVitals(console.log))
    // or send to an analytics endpoint. Learn more: https://bit.ly/CRA-vitals
    reportWebVitals();
  }


//Token Refresh
  setInterval(() => {
    keycloak.updateToken(70).then((refreshed) => {
      if (refreshed) {
        console.info('Token refreshed' + refreshed);
      } else {
        console.warn('Token not refreshed, valid for '
          + Math.round(keycloak.tokenParsed.exp + keycloak.timeSkew - new Date().getTime() / 1000) + ' seconds');
      }
    }).catch(() => {
      console.error('Failed to refresh token');
    });
  }, 1000)

}).catch(() => {
  console.error("Authenticated Failed");
});