nixos/nginx: re-enable ssl_session_tickets

[bmillwood]

Mozilla's recommendations no longer include this item. Per mozilla/server-side-tls#135 and
mozilla/ssl-config-generator#252, it sounds like versions of nginx prior to 1.23.2 (released 2022-10-19) didn't make it easy to properly rotate the ticket encryption keys, but since that version it's now done automatically. Since nixos-24.05 is already on nginx-1.26.2, it seems safe to remove this option.

I came across this while looking to see what was included in recommendedTlsSettings and noticing that it had fallen out of sync with its own source. I don't personally feel strongly that ssl_session_tickets is important to set one way or the other, this just seems like housekeeping to me. I believe it has performance implications (reducing the amount of memory nginx needs?) but the docs are not very helpful.

One other notable difference between the Mozilla settings and ours is Mozilla enables HSTS. I don't know if this is not included because it's new or if it's omitted intentionally, but I decided not to include it here because it seems like it could be a more significant / impactful / client-facing change. Let me know if we want it and I might do a followup PR, perhaps adding it as an option.

Things done

• Built on platform(s)
  • x86_64-linux -- well, actually I cherry-picked onto nixos-24.05 and then built that, but I imagine that's sufficient?
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true (because it's the default on Linux and I haven't overridden it)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[emilazy]

I’m a little nervous about the compromise to forward secrecy posed by session tickets, but if we’re tracking Mozilla’s recommendations here then it makes sense to match the update.

I think we should not enable HSTS out of the box since it is the kind of policy decision that is hard to revert and can cause painful availability issues. An option for it might be nice though.

[bmillwood]

I’m a little nervous about the compromise to forward secrecy posed by session tickets, but if we’re tracking Mozilla’s recommendations here then it makes sense to match the update.

Equally happy to update the comment to say that we're not following Mozilla's recommendations, I don't have a horse in that race :)

I think we should not enable HSTS out of the box since it is the kind of policy decision that is hard to revert and can cause painful availability issues. An option for it might be nice though.

Cool. I'll probably make a separate PR adding the option. (edit: #350302)

[bmillwood]

@emilazy do you want to choose something to happen here?

[janbrasna]

Feel free to feed any concerns back to us @mozilla/ssl-config-generator via issues or discussions — chances are if it's not good enough for you, it probably won't be for others, too;)

it sounds like versions of nginx prior to 1.23.2 (released 2022-10-19) didn't make it easy to properly rotate the ticket encryption keys, but since that version it's now done automatically.

Their changelog makes it sound it's safe now, but from the mailinglist changeset it looked more like just a better GC at first glance — but I will look more deeply into what's the actual change: it's the OCT '22 commits here: https://github.com/nginx/nginx/commits/release-1.23.2/ if you want to inspect yourselves if that's reasonably safe for PFS.

One other notable difference between the Mozilla settings and ours is Mozilla enables HSTS. I don't know if this is not included because it's new or if it's omitted intentionally, but I decided not to include it here

It's been around for years, but for these exact concerns downstream the HSTS is only behind a preference to help emit the correct headers and time spans, but also make it easy to consume configs without these.