I think it's useful to use the "shared cache" naming — RFC 2616 distinguishes between "shared" and "non-shared" caches. While this change is only applying the bit of that distinction related to `Cache-Control: private`, there are other behavior differences the RFC calls for (e.g., the treatment of requests with an Authorization header) which faraday-http-cache might want to implement later. Since those behavior differences would all fall under the shared-vs-non-shared distinction in RFC 2616, naming the flag something with "shared cache" now (and making clear the practical implications in the docs) seems more future-proof.