Server side image uploads

We are trying to implement an image upload from our server.
We need to replicate the form submit from the [direct-upload example](https://github.com/dwyl/image-uploads/blob/master/examples/direct-upload/public/client.js#L34) on the back end but we're having trouble structuring our http POST request.
The form data that we want to send are the [params](https://github.com/dwyl/image-uploads/blob/master/examples/direct-upload/generate-credentials.js#L19) returned from our `getS3Credentials` function.
The url of the form is the [endpoint url](https://github.com/dwyl/image-uploads/blob/master/examples/direct-upload/generate-credentials.js#L18) from the same function.

Our form looks like this:

``` html

Submit
```

And this is what we're dynamically adding before we submit the form:

``` js
function buildAndSubmitForm (s3Data) {
var form = document.querySelector('form')
var keyInput = document.createElement('input')
keyInput.setAttribute('type', 'hidden')
keyInput.setAttribute('name', 'key')
keyInput.setAttribute('value', s3Data.filename)
form.setAttribute('method', 'post')
form.setAttribute('action', s3Data.endpoint_url)
form.setAttribute('enctype', 'multipart/form-data')
form.insertBefore(keyInput, form.firstChild)
form.url = s3Data.endpoint_url
form.formData = s3Data.params
form.submit()
}
```

Does anyone know how our POST request should look in order for our form data to be sent in the same fashion as our front end example?