title: Angular 2 form data to Express CORS issue
body: <p>I'm trying to upload some files to an Express server, the server is using the cors() module like this</p>
  
  <pre><code>app.use(cors());
  </code></pre>
  
  <p>this is the Angular 2 code to upload the files</p>
  
  <pre><code>let formData:FormData = new FormData();
      for(let i = 0; i &lt; files.length; i++) {
          let file = files[i];
          formData.append(`file`+(i+1), file, file.name);
      }
  
      let token = localStorage.getItem('supersecrettoken');
      let headers = new Headers();
      headers.append("Content-Type", 'multipart/form-data');
      headers.append("auth", token);
  
      return this.http.post(`${Constants.SERVER_IP}/imports`, formData, {headers: headers})
          .map(response =&gt; {
              return response.json();
          })
          .catch(this.logger.handleError).share();
  </code></pre>
  
  <p>Now this returns the following error</p>
  
  <pre><code> No 'Access-Control-Allow-Origin' header is present on the requested resource
  </code></pre>
  
  <p>If I change the multipart/form-data to application/json it will work.</p>
  
  <p>How can I upload multiple files to the server then?</p>
  
  <p>Regards!</p>