Closed
Description
RFC 4648 defines several encodings, including "base64url", which should be usable with contentEncoding. Currently, that keyword only references RFC 2045 §6.1, which (with some persistence) leads to the IANA registry for Transfer Encodings.
Notably, this registry only includes the 2045 encodings and not the 4648 ones, or any others. It is controlled by RFC 4289, which is specifically about MIME transfer encodings.
From what I can make out of 4648, it's arguably more relevant to modern web APIs. Also, it explicitly sets out to make "base64" more consistent and usable, so we probably want 4648's "base64" over 2045's. I think?