Hi!
here is the snuppet of configuration I use for uploading:
location /upload {
auth_request /auth;
upload_pass /200;
upload_store /download 1;

upload_resumable on;

#Return download path to calling party in custom header value
upload_add_header XXX-DownloadURI "$upload_tmp_path";
#Return md5 file checksum to calling party as custome header value
upload_add_header X-XXX-MD5SizeChecksum "$upload_file_md5";
upload_add_header X-XXXXr-FileSize "$upload_file_size";

upload_aggregate_form_field "$upload_field_name.md5" "$upload_file_md5";
upload_aggregate_form_field "$upload_field_name.size" "$upload_file_size";

It works perfect, great job, thanks! Specially about upload_add_header.
However the MD5 hashes returned in response header are.. not hashes.
They are:
34383765656261393461336230613362 OR
34396436323764343839623564646664
I can't rely on them on caller side..

Could it be a problem with add_header? I assume that aggregate field is generated correctly, however when setting it to header via upload_add_header, there is an convertion mistake.

Many thanks in advance!
You are doing great Job