Challenge 2: Should /api/private/ Join the Same Cache Zone? — Solution Walkthrough

The answer:

No — not the same way /api/public/ was configured, and not without
real changes if it's cached at all.

Why, per this course's own material:

Chapter 7's own cache-key material and warning box establish that
genuinely personalized, per-user content caught under the default (or
even the capstone's own /api/public/) cache key can be served to the
wrong user entirely, since the key doesn't vary by identity. /api/private/
is explicitly described as requiring authentication and returning
genuinely personalized data per user — exactly the scenario Chapter 7
warned against caching under a shared key.

What would actually be needed if caching were still desired:

Either exclude /api/private/ from caching entirely via proxy_no_cache
(the simpler, safer default), or, if caching is genuinely valuable for
this endpoint, add an identity-aware component (such as
$cookie_session_id) directly into a dedicated proxy_cache_key for that
location — never reusing the same api_cache zone and key configuration
used for /api/public/ without that change, since doing so risks the
exact cross-user data leak Chapter 7's own warning box described.

WHY THIS WORKS AS AN ANSWER
------------------------------
This exercise applies Chapter 7's own cache-key and personalization
material to a new endpoint introduced specifically in this capstone,
correctly refusing to extend the existing cache configuration
uncritically just because it worked for a different, non-personalized
endpoint.