title: Facebook token_url parameter
body: <p>I am using a module for Facebook login in my app using <code>Electron.js</code>. However there is a <code>tokenUrl</code> parameter that I could not find what I should put for it: 
  here is the code</p>
  
  <pre><code>const config = {
  clientId: environment.FACEBOOK_APP_ID,
  clientSecret: 's494df4sd6f4984984984',
  authorizationUrl: 'https://www.facebook.com/v2.8/dialog/oauth',
  tokenUrl: '??????',
  useBasicAuthorizationHeader: false,
  redirectUri: "https://www.facebook.com/connect/login_success.html"
  
  
  };
  </code></pre>
  
  <p>the <code>token_url</code> for google works for perfect, but not for Facebook. here is the Google <code>token_url</code>:</p>
  
  <pre><code> tokenUrl: 'https://accounts.google.com/o/oauth2/token',
  </code></pre>