Ok, so I have an API service, that I am building into a container. I'm looking for a service/provider that will host it, and provide all the front-end pieces - e.g., authentication/token, usage-tracking/quotas, firewall/security. Is there such a beast and I'm just daft and can't see the forest for the trees?
You may want to look for PaaS.
Here are easier, but with less features (should be fine for what you're are building):
Steeper learning curve, but much more capable:
All of them can run docker images.
This can be interpreted differently, as I understand you want a separate service to handle your authentication. In that case look for identity and access management solutions. Auth0 would be a good start.
You will need two separate services. The first "running" your code/containers/servers. There are quite a lot of providers for this, including the big cloud providers. The other one, providing all the "API services" on top, is more scarce. Last time, I tried RapidAPI and it did the trick for me. It also handle payments which you strangely omitted from your list although it is a big chunk. ...of course, it goes without saying that the firewall/security part should be done on the container/networking side. Good luck
By container you mean docker? If yes, then did you search "Docker hosting"?
Ha, that's funny. No, I don't mean docker. I mean API, specifically. Just happens to be packaged as a container.
So what container you talk about? Docker is most used type of container nowadays.