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Livio Spring
f0329f0298
# Which Problems Are Solved
The `/.well-known/apple-app-site-association` and
`/.well-known/assetlinks.json` responses are instance specific: the body
depends on the requested host. The responses did not declare this, so a
shared cache whose cache key does not include the host could store one
instance's file and serve it on another instance's domain. This could
result in a wrong or empty file being returned intermittently, breaking
native passkey verification.
Dropping the `public` directive (#12634) was not sufficient: depending
on its cache mode, a shared cache may store any response carrying a
`max-age`.
The docs page for native app links also still documented the old
`Cache-Control: public` header and only the single `get_login_creds`
relation (missing `handle_all_urls`, added in #12634).
# How the Problems Are Solved
- Send **`Vary: Host`** on both well-known responses, declaring that the
body depends on the host: a spec-compliant shared cache must store
per-host variants or skip caching. Clients addressing a single host (the
Apple and Google verifiers, browsers) are unaffected and keep honoring
the configured `max-age`.
- Correct the outdated caching reasoning in the code comments.
- Guard the header with unit and integration tests.
- Update the native app links docs page: both Digital Asset Links
relations and the current response headers.
# Additional Changes
None. `WellKnown.AppLinksCacheControlMaxAge` behavior is unchanged (`0`
still results in `no-store`).
# Additional Context
- Follow-up to #12634; relates to #12497.
- Verified with interleaved requests against two instances: responses
are no longer reused across domains, and each domain consistently serves
its own configuration.
- To be cherry-picked to `v4.x` from `main` once merged.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
---------
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit c9d747d407)