$ curl -v https://docker.pkg.github.com/v2/ 2>&1 | grep -i www-auth
< Www-Authenticate: Basic realm="GitHub Package Registry"

version: '3.7'

networks:
  cache:
    name: cache

volumes:
  github-cache:
    name: github-cache

services:
  github-cache:
    image: registry:2
    restart: unless-stopped
    environment:
      REGISTRY_LOG_LEVEL: debug
      REGISTRY_STORAGE_FILESYSTEM_ROOTDIRECTORY: /var/lib/registry
      REGISTRY_PROXY_REMOTEURL: https://docker.pkg.github.com
      REGISTRY_PROXY_USERNAME: $GITHUB_USER
      REGISTRY_PROXY_PASSWORD: $GITHUB_TOKEN
      REGISTRY_HTTP_TLS_CERTIFICATE: /host/reg.pem
      REGISTRY_HTTP_TLS_KEY: /host/reg-key.pem
    networks:
    - cache
    volumes:
    - type: bind
      source: .
      target: /host
      read_only: true
    - type: volume
      source: github-cache
      target: /var/lib/registry
  builder:
    image: docker:dind
    command: ["--registry-mirror", "https://hub-cache:5000", "--debug"]
    privileged: true
    restart: unless-stopped
    networks:
    - cache
    volumes:
    - type: bind
      source: ./ca.pem
      target: /etc/docker/certs.d/github-cache:5000/ca.crt
      read_only: true

docker-compose up -d
docker-compose exec builder sh
docker pull busybox
docker tag busybox docker.pkg.github.com/$username/$project/busybox:latest
docker login docker.pkg.github.com
docker push docker.pkg.github.com/$username/$project/busybox:latest
docker pull github-cache:5000/$username/$project/busybox:latest