title: Angular $http not sending header in OPTIONS pre-flight
body: <p>I'm trying to connect to an API with the $http service that requires a certain header to be defined for <code>POST</code> requests:</p>
  
  <pre><code>app.run(['$http', function($http) {
      $http.defaults.headers.post.hello = 'world';
  }]);
  </code></pre>
  
  <p>However, my Angular app sends an <code>OPTIONS</code> request before the <code>POST</code>, and it does not appear to be sending the custom-defined header.</p>
  
  <p>Check out the network tab in this Plunker: <a href="http://plnkr.co/edit/tcqIb2q9zIQb3nf2SzyT" rel="nofollow noreferrer">http://plnkr.co/edit/tcqIb2q9zIQb3nf2SzyT</a></p>
  
  <p>And watch see that where the request is supposed to send a <code>hello</code> header with the value of <code>world</code>, it actually isn't:</p>
  
  <p><img src="https://i.stack.imgur.com/rdiWi.png" alt="enter image description here"></p>
  
  <p>I see the <code>hello</code> in the <code>access-control-request-header</code>, but shouldn't it be on its own line? And why doesn't it send the value <code>world</code>?</p>