Option to restrict gateway to only serve locally available / cluster content

I'm investigating the suitability of IPFS as a server side file storage and distribution medium.

I can manage, upload and pin files through the HTTP REST API (:5001). I would like to have the stored files available both through the IPFS network and through HTTP. The gateway seems like an easy, simple solution to provide the files directly through HTTP with good latency to the user (and would possibly be reverse proxied through NGINX and/or a third-party CDN as well).

The only issue is, I couldn't find a way to limit it to only provide locally pinned content. Making a custom intermediate server to filter out requests seems unnecessary and would require maintaining a duplicate (and probably inefficient) index into the IPFS datastore. Since it might serve millions of files, maintaining a gigantic `ipns`-based ipld document to index the files also seems wasteful and inefficient (and a possible privacy issue if directory content is exposed).

I'm not interested (at this time) in creating a private network, using `--offline` or using custom bootstrap nodes, since I want to data to be available through the public IPFS network as well.

I believe this "dual-stack" approach might be reasonably classified as "plausible" (given that IPFS matures to the point it provides sufficient value to be used in mainstream projects), so I decided to publish it here as a feature request (in case it is not already available! in that case I'd be really happy to know how to achieve this!)

(_Edit_: as a natural extension, it would probably also be useful to have an option to only serve content pinned by a cluster of servers -- thus any node in the cluster could act as a restricted IPFS gateway - that only serves content hosted within the cluster itself)