Simplest form file uploader.
It just saves uploaded file from HTML form to the new file on the disk.
Also it calculates BLAKE2s checksum, replying with it in the answer.

You can upload files with curl:

    curl -F fileupload=@somedata.tar.gpg http://localhost:8086/upload/

You can verify integrity locally:

    b2sum -a blake2s somedata.tar.gpg