Expose Docker Container services on the Internet using the ngrok docker image

The challenge: you are running a service, API or web application in a Docker container, locally on your laptop or in a cloud based VM or container platform. You would like to provide access to external consumers — yourself on your smart phone, a piece of code running in a cloud environment, a colleague on your local network or on the other side of the world. The question is: how to get requests from these external parties to the application that does not and cannot [easily] expose and external endpoint.