Add your self signed cert to the list of trusted certificates on the host. For some reason, docker doesn't use the certificates on the daemon for this authentication. Here are the commands for a debian host:
sudo mkdir -p /usr/local/share/ca-certificates
sudo cp ca.pem /usr/local/share/ca-certificates/ca-local.crt
sudo systemctl restart docker
The docker restart at the end is required for the daemon to reload the OS certificates.