Previously, any HTTP request to an endpoint that included a principal
would bypass the cache. This prevented authenticated requests from
making use of the cache and its configurable time-to-live.

This commit updates the caching operation invoker to include the
principal, if any, in its cache key. As a result, requests that
include a principal will make use of the cache, potentially returning
the result of a previous invocation of the same endpoint by the same
principal.

Closes gh-19538