Came across this: Authenticated and private feed, the other day. Building authentication, authorization and security into the feed reader is one way to go. But, this effort would have to be replicated across all the feed platforms out there.
A better way would be to leave these platforms to do one thing well, and push the aforementioned functionality into a web services intermediary, like SOA Software's Network Director, which supports HTTP Basic Auth and role-based subscriptions to feeds.
In addition, it also supports digital signatures (signing and verification) on feeds, and tag-based aggregation of these feeds. This is the ability to define a virtual ("aggregate") feed, which is a boolean expression on the tags (or labels) applied to the underlying ("concrete") feeds. For e.g., if the New York Times feed is tagged "nyt" and the Wall Street Journal feed is tagged "wsj", one could define a new aggregate feed called "news", defined as (nyt OR wsj).