title: Access request headers in doPost()
body: <p>To verify a webhook i need to get a parameter from the request headers. So far i couldn't find any information if it is actually possible to access these headers within Apps Scripts. Only thing that works so far is accessing the body of the post request.</p>
  
  <pre><code>function doPost(e) {
      // something like this
      var headerParam = e.headers['Content-Type'];
      // ...
  }
  </code></pre>