The Proton's /pdf endpoint does not return etag nor last-modified headers. For caching purposes, all services should return at least one - last-modified or etag header.
The etag caching doesn't fully apply for proton the way it applies to other services - as cache expiration is set to 600 seconds both for client and varnish. Once the cache expires at the client, it also expires on varnish.
- Acceptance criteria
- Proton renders return the LastModified header
- If MediaWiki/any other instance do not return the LastModified, Proton will use the current system time and return it as LastModified.