public/index.html

<!DOCTYPE html>
<html>

<head>
        <meta charset="utf-8" />
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title>Node OAuth2 Demo</title>
        <meta name="viewport" content="width=device-width, initial-scale=1">
</head>

<body>
        <a id="login">Login with GitHub</a>

<script>
  // fill in your cliend_id
  const client_id = '7e015d8ce32370079895';

  const authorize_uri = 'https://github.com/login/oauth/authorize';
  const redirect_uri = 'http://localhost:8080/oauth/redirect';

  const link = document.getElementById('login');
  link.href = `${authorize_uri}?client_id=${client_id}&redirect_uri=${redirect_uri}`;
</script>

</body>

</html>