URL, URI and the w3c

Dear all,

I noted that some specs reference  URL/URI from https://url.spec.whatwg.org/
while others use https://www.rfc-editor.org/rfc/rfc3986 & co.

This can be relevant if you need normative references to e.g. percent encoding
and/or application/www-form-urlencoded where IANA media type registration
references https://url.spec.whatwg.org/


Which is the rationale for filing a specification under the w3c with
respect to the IETF?
I assume that those specs are aligned, isn't it?
Which is the organization that ensures that alignment?
Which spec should I reference in an HTTP derived protocol
such as OAuth2 ?

Thanks and have a nice day,
R.