Time is short so don't do this now but I suggest reaching out to Justin Richer about HTTP signatures to see if they might benefit from some problem types too. See https://httpwg.org/specs/rfc9421.html#rfc.section.1.4 and specifically
If the response is from an HTTP API, a response with an HTTP status code such as 400 (Bad Request) could include more details [RFC7807][RFC9457], such as an indicator that the wrong key material was used.
That's a good idea. I will reach out to Justin and see if there is interested to do so. Maybe there is the potential to share problem types between digests and signatures.
Time is short so don't do this now but I suggest reaching out to Justin Richer about HTTP signatures to see if they might benefit from some problem types too. See https://httpwg.org/specs/rfc9421.html#rfc.section.1.4 and specifically