Send a CSV file from Ember Js to Rails using Ajax

I'm trying to upload a csv file with ajax from Ember Js and read it in my Rails application. I've tried two different approaches. In the first one I tried to send the file from Ember like this:

submitImport() {
  var fd = new FormData();
  var file = this.get('files')[0];
  fd.append("csv_file", file);
  return this.get('authAjax')
    .request('/contacts/import/csv', {
      method: 'POST',
      processData: false,
      contentType: false,
      data: fd 
    });
}

but the problem is that I don't get the csv_file param in the rails application. The request.content_type is application/x-www-form-urlencoded and I need multipart form. I could use reques.raw_post but then I get something like this ------WebKitFormBoundarymgBynUffnPTUPW3l\r\nContent-Disposition: form-data; name=\"csv_file\"; filename=\"elevatr_import.csv\"\r\nContent-Type: text/csv\r\n\r\ngeorgica,gica@me.com\nleo, leonard@yahoo.com\ngigel, becali@oita.fcsb\n\r\n------WebKitFormBoundarymgBynUffnPTUPW3l--\r\n and I would need to somehow parse this, and I don't really like this solution.

The other approach was to send the file base64 encoded and then decode it from Rails. I've tried this:

`

submitImport() {
  var fd = new FormData();
  var file = this.get('files')[0];
  this.send('getBase64', file);
  var encoded_file = this.get('encoded_file');

  return this.get('authAjax')
    .request('/contacts/import/csv', {
      method: 'POST',
      data: { csv_file: encoded_file }
    });
},
getBase64(file) {
  var controller = this;
  var reader = new FileReader();
  reader.readAsDataURL(file);
  reader.onload = function () {
    controller.set('encoded_file', reader.result);
  };
}

But for some reason, the post request is submitted first and only after that the getBase64 method is called. Does anyone knows why is this happening or if I should use a different approach?

Thanks