Last Call Review of draft-ietf-privacypass-protocol-12
review-ietf-privacypass-protocol-12-httpdir-lc-nottingham-2023-08-30-00

Reviewing purely from the perspective of how this document uses HTTP>

* Given that 'This document describes the issuance protocol for Privacy Pass
built on [HTTP]', I suspect it should be a normative reference.

* 'The Issuer directory and Issuer resources SHOULD be available on the same
domain.' Is "domain" a _hostname_, _origin_, or something else, e.g., using the
Public Suffix List?

* 'Issuers SHOULD use HTTP caching to permit caching of this resource
[RFC5861].' Either 'SHOULD use HTTP cache directives...' or 'SHOULD permit
caching..'.

* Examples use HTTP/2; the style guide recommends using HTTP/1.1 for all
examples except for those that are specific to a protocol version. See:
<https://httpwg.org/admin/editors/style-guide>

* It's not necessary to specify Cache-Control on POST requests.

* 'If any of these conditions is not met, the Issuer MUST return an HTTP 400
error to the client.'

  - HTTP status codes should be spelled out; e.g., "400 (Bad Request)".

  - 422 (Unprocessable Content) might be a better status code to use here,
  though -- 400 will be used by generic HTTP software for problems at that
  layer, and so you won't be able to distinguish those problems from these more
  specific ones.

  - Also, we generally encourage using SHOULD when specifying a status code
  like this, so that clients don't form the view that they can depend on seeing
  this status code in this situation (they can't; intermediary and other
  software may change the status code).

  - Have you considered defining one or more HTTP problem types (RFC9457) to
  provide more granularity and detail?