We have developed this file upload feature purely from a backend Express application perspective. However, supporting multipart/form-data encoding as part of a <input type="file"> isn't very complicated to implement on the frontend:

<form action="http://localhost:3000/api/login" method="post" enctype="multipart/form-data">
  <input type="file" name="cover">
  <button type="submit">Submit</button>
</form>

This sort of file upload support has existed in web browsers since the HTML 4 spec, so there is a lot of supplemental information available online about this topic.