ACME semantic variances in WFE2

This is an issue I have asked Claude to put together as a result of its audit of Boulder against the RFCs Boulder implements.

Checklist of cases where Boulder emits a field the RFC defines but its
meaning, status code, or population logic diverges from the spec.
Distinct from the "non-standard fields to remove" and "missing fields to
add" lists — every item here is a field Boulder already implements and
already sends on the wire, but with the wrong semantics.

• unauthorized problem returns HTTP 403 instead of 401 for
  deactivated accounts. RFC 8555 §7.3.6: "If a server receives a
  POST or POST-as-GET from a deactivated account, it MUST return an
  error response with status code 401 (Unauthorized) and type
  urn:ietf:params:acme:error:unauthorized." Boulder's
  Unauthorized helper hardcodes http.StatusForbidden, and the JWS
  verification layer raises berrors.UnauthorizedError for
  deactivated accounts, which the web layer maps to HTTP 403. The
  type URN is correct; the status code is not. Deactivated-account
  rejections are the specific case the RFC calls out as MUST-401.
  probs.Unauthorized
  · wfe2/verify.go deactivated-account check
  · web/probs.go berrors→HTTP mapping

• NotFound helper emits malformed problem type on 404
  responses. RFC 8555 §6.7 defines malformed as "The request
  message was malformed" — a 400-class validation error. Boulder's
  probs.NotFound builds a ProblemDetails with
  Type: MalformedProblem and HTTPStatus: 404. Every 404 raised
  from WFE2 (finalize, certificate download, authorization lookup,
  order lookup, revocation) carries a type URN that tells the
  client "your request was syntactically bad" when the actual
  condition is "that resource does not exist".
  probs.NotFound

• prepChallengeForDisplay marks every challenge invalid when
  the authz is invalid. RFC 8555 §7.1.4: "For invalid
  authorizations, the challenge that was attempted and failed." The
  RFC models a single failing challenge driving the authz to
  invalid. Boulder instead overwrites the status of every
  challenge on the authz to invalid, including challenges the
  client never attempted. The error field is still only populated
  on the actually-attempted challenge, so a client cannot tell from
  status alone which challenge failed, and the status/error fields
  become inconsistent across the challenge array.
  prepChallengeForDisplay invalid broadcast

• order.expires serializes zero-valued time when unset. RFC
  8555 §7.1.3: "expires (optional, string): … This field is
  REQUIRED for objects with 'pending' or 'valid' in the status
  field." Optional fields that are unset should be absent from the
  response, not serialized as a placeholder. Boulder's
  orderJSON.Expires is a bare time.Time with no omitempty and
  no pointer indirection, so any code path producing an order
  without an expiry emits "expires": "0001-01-01T00:00:00Z",
  claiming the order expired in year 1 AD. In practice every
  Boulder order has a real expiry; the type permits a state that
  would silently publish nonsense.
  orderJSON.Expires

• updateAccount returns 200 OK for contact updates it silently
  discards. RFC 8555 §7.3.2 describes the account-update flow: a
  client POSTs changed fields and the server returns 200 (OK) with
  "the resulting account object". A 200 with the updated object
  implies the update was accepted. Boulder's updateAccount
  dispatches on status: for deactivated it deactivates, for
  valid or empty it returns the account unchanged with the
  explanatory comment "They probably intended to update their
  contact address, but we don't do that anymore, so simply return
  their account as-is. We don't error out here because it would
  break too many clients." A client comparing the echoed account
  against what it sent has no signal that its contact update was
  ignored.
  updateAccount valid branch

• KeyRollover 409 uses the non-standard conflict URN. RFC
  8555 §7.3.5: "If there is an existing account with the new key
  provided, then the server SHOULD use status code 409 (Conflict)
  and provide the URL of that account in the Location header
  field." The RFC pins the HTTP status and the Location header
  but does not define a problem type for this condition, and §6.7
  has no registered URN for it. Boulder calls probs.Conflict on
  both the pre-check and the post-update-race branch of
  KeyRollover, emitting urn:ietf:params:acme:error:conflict — a
  URN not in the §6.7 registry. The 409 status and Location header
  are correct; the URN is semantically a Boulder invention for a
  well-defined RFC condition.
  KeyRollover pre-check
  · KeyRollover race branch
  · probs.ConflictProblem

• RenewalInfo endpoint accepts POST in addition to GET. RFC 9773
  §4.1: "the client sends an unauthenticated GET request to a path
  under the server's renewalInfo URL." §6 reinforces: "RenewalInfo
  resources are exposed and accessed via unauthenticated GET
  requests, a departure from the requirement in RFC 8555 that
  clients send POST-as-GET requests to fetch resources from the
  server." The RFC's request-method contract is singular: GET only,
  unauthenticated. Boulder registers the renewalInfo endpoint for
  both GET and POST. Accepting POST isn't explicitly forbidden, but
  it departs from the stated method contract, and the POST path
  bypasses the caching-friendliness rationale §6 gives for making
  the endpoint GET-only.
  RenewalInfo handler registration

• Certificate download ignores the Accept header. RFC 8555
  §7.4.2: "The ACME client MAY request other formats by including
  an Accept header field in its request… Server support for
  alternate formats is OPTIONAL." HTTP content negotiation
  semantics (RFC 9110) additionally imply that a server which cannot
  satisfy a specific Accept value should respond 406 (Not
  Acceptable). Boulder's Certificate handler ignores the Accept
  header entirely and unconditionally sets
  Content-Type: application/pem-certificate-chain. A client
  sending Accept: application/pkix-cert (or any other value
  excluding pem-certificate-chain) receives a 200 with PEM anyway,
  with no signal that its stated preference was ignored.
  Alternate-format support being optional is fine; silently
  overriding the client's explicit Accept value is not the
  content-negotiation contract the RFC points at.
  Certificate handler Content-Type

Start by reading the cited entry points in probs/probs.go, wfe2/verify.go, wfe2/wfe.go, and web/probs.go, then compare each unchecked behavior with its referenced RFC section. The work is complete when every selected variance has an agreed correction and its response status, problem details, serialization, or method behavior is verified against the specification.