The built-in Nginx core upload functionality (aka client_body_in_file_only) is not well known way to go due to lack of knowledge base. It does not support multipart/form-data, but AJAX or direct binary upload from mobile devices. In your case AJAX upload with conjunction of client_body_in_file_only is the best solution. The second advantage is to having authentication check before the request is being processed.
The built-in Nginx core upload functionality (aka client_body_in_file_only) is not well known way to go due to lack of knowledge base. It does not support multipart/form-data, but AJAX or direct binary upload from mobile devices. In your case AJAX upload with conjunction of client_body_in_file_only is the best solution. The second advantage is to having authentication check before the request is being processed.
I would like to recommend to extend README file or Wiki to spread knowledge how to use it. I shared few bits and bobs on Coderwall, maybe useful: https://coderwall.com/p/swgfvw/nginx-direct-file-upload-without-passing-them-through-backend