Running
Deploy to cloud run (will fail first time)
gcloud run deploy
Set environment variable PROXY_TO to whatever you want the proxy to be pointing to and redeploy the service.
Set environment variable AUTH_TOKEN in case you want to add extra header to authenticate proxy on your destination.
Local testing
docker build -t test .
docker run -e PROXY_TO=https://127.0.0.1 -it test
docker run -e AUTH_TOKEN="1234" -e PROXY_TO=https://127.0.0.1 -it test