title: set withCredentials to the new ES6 built-in HTTP request API : Fetch
body: <p>How to set <code>withCredentials=true</code> to  <a href="https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch" rel="noreferrer"><code>fetch</code></a> which return promise.
  Is the following correct : </p>
  
  <pre><code>fetch(url,{
     method:'post',
     headers,
     withCredentials: true
  });
  </code></pre>
  
  <p>I think the <a href="https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API/Using_Fetch" rel="noreferrer">MDN documentation</a> talked about everything about http-requesting except this point: <code>withCredentials</code> </p>