gistfile1.txt

import React from 'react';
import ReactDOM from 'react-dom';
import { BrowserRouter, Switch, Route, Link, Redirect } from 'react-router-dom';

function Auth() {
  return false;
}

const Admin = () => (
  <h1>This is Admin page</h1>
)

const Login = () => (
  <h1>Login Page</h1>
)

const Home = () => (
  <h1>Home Page</h1>
)

const ProtectedRoute = ({ component: Component, ...rest }) => (
  <Route {...rest} render={(props) => (
    Auth() === true
      ? <Component {...props} />
      : <Redirect to='/login' />
  )} />
)

const App = () => (
  <>
    <ul>
      <li>
        <Link to="/">Home</Link>
      </li>
      <li>
        <Link to="/admin">Admin</Link>
      </li>
    </ul>
    <Switch>
      <Route exact path="/" component={Home} />
      <Route path="/login" component={Login} />
      <ProtectedRoute path="/admin" component={Admin} />
    </Switch>
  </>
)

ReactDOM.render(
  <BrowserRouter>
    <App />
  </BrowserRouter>,
  document.getElementById('root')
);