It just (re)occurred to me that specs defining new HTTP headers (which the cool kids call fields nowadays) are supposed to request their registration in the Hypertext Transfer Protocol (HTTP) Field Name Registry. I don't want to hold up this PR for this but will create an issue from this comment so as not to lose track of it.
Originally posted by @bc-pi in https://github.com/vcstuff/draft-ietf-oauth-attestation-based-client-auth/issues/74#issuecomment-2123037858