Hi Ryan,
Apologies for the very late reply.
I accept your comments below, and we will reword this section as a
recommendation or best practice. The flexibility of CAA means that the solution
must be tailored to the particular CA(s) trusted by the IdO. This is
unfortunate in the sense that we cannot recommend a one-size-fits-all security
solution, and admins would need to have deeper understanding of the mechanisms
they are using.
I am wondering though about this sentence: A CA can "also offer additional
validation methods/issuance flows which also use the "dns-01" method." Doesn't
specifying "dns-01" restrict the CA to one particular validation/authorization
flow?
Thanks,
Yaron
On 29/08/2019, 12:38, "Thomas Fossati" <[email protected]> wrote:
Hi Ryan,
Thanks very much for the comments. I'm going to address some of your
points and let Yaron comment on the rest.
[snip]
> 6.1 Restricting CDNs to the Delegation Mechanism There are RFC 2119
> MUSTs attached here, when it seems these functionally should be
> SHOULDs. That is, I think it's fair to highlight the consideration of
> concerns between the IdO and the CDN, but I don't think it's
> reasonable to normatively specify the policy consideration mechanism.
> For example, as specified, those requirements would not be sufficient
> to guarantee that a conforming CA uses this mechanism, as a number of
> CAs "comply with ACME" (second bullet), but also offer additional
> validation methods/issuance flows which also use the "dns-01" method.
>
> As CAA is intentionally flexible to allow for CA-specific policy
> identifiers to be expressed between the IdO and the CA, I think it's
> best to change these to SHOULD, and to recognize that CAs may devise
> other means of technically expressing this conformance, and that's
> between the IdO and the CA. CAA provides the necessary component (to
> allow them to restrict to CAs that respect CAA, to allow CA-specific
> policy), but I think that's the extent to which policy-specific
> requirements can be made.
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