This is for running a container of sshd to allow uploading files. To start, use:

/usr/bin/docker run --rm \
  -p ${port}:22 \
  -v /path/config:/config:ro \
  -v /path/srv:/srv \
  -e USER=${username} \
  tunathu/sshd

, where /path/config contains ssh_host_{dsa,ecdsa,rsa}_key{,.pub} for the host key of the container and authorized_keys for the public keys allowed to login. All the files in /path/config shall be owned by root. /path/srv is an example for the location where the login users can store files.