Proposed changes

Fixes #656 ; Ability to set file permissions for uploads when using client_body_temp_path

verified to work with config

    location / {
        proxy_pass http://localhost:8000/;

        client_body_temp_access group:rw;
        client_body_in_file_only clean;
        proxy_set_header X-File $request_body_file;
        proxy_set_body off;
    }

Commit message / PR description updated to correctly reference issue.

What is the exact purpose?

Note: this is used to store temporary files on disk, in case the request body doesn't fit in memory, i.e. is larger than client_body_buffer_size.
They are removed once the request is processed.

The specific use case is detailed in issue #656, @pluknet

Apparently, others have also wanted this feature:

https://stackoverflow.com/questions/54708301/linux-client-body-in-file-only-how-to-set-file-permissions-for-the-temp-file
https://trac.nginx.org/nginx/ticket/1651