[cabf_validation] Clarifying Acceptable Status Codes for Following Redirects in methods 18 and 19

Mon Jun 22 10:26:46 MST 2020

I made some changes to methods 18 and 19 regarding following redirects, and wanted to get everyone’s thoughts before putting them into a ballot.

Here is the current text:

> If the CA follows redirects the following apply:

> 1.         Redirects MUST be initiated at the HTTP protocol layer (e.g. using a 3xx status code).

> 2.         Redirects MUST be the result of an HTTP status code result within the 3xx Redirection class of status codes, as defined in RFC 7231, Section 6.4.

> 3.         Redirects MUST be to resource URLs with either via the "http" or "https" scheme.

> 4.         Redirects MUST be to resource URLs accessed via Authorized Ports.

This is what the text will change to:

> If the CA follows redirects the following apply:

> 1.         Redirects MUST be initiated at the HTTP protocol layer (e.g. using a 3xx status code).

> 2.         Redirects MUST be the result of a 300, 301, 302, 303, 307, or 308 HTTP status code response. Other status codes MUST NOT be treated as being equivalent to the 300 status code.

> 3.         Redirects MUST be to resource URLs contained in the Location HTTP response header.

> 4.         Redirects MUST be to resource URLs with either via the "http" or "https" scheme.

> 5.         Redirects MUST be to resource URLs accessed via Authorized Ports.

Niko Carpenter 
Software Engineer

From: Tim Hollebeek <tim.hollebeek at digicert.com>
Date: Friday, April 24, 2020 at 15:55
To: Ryan Sleevi <sleevi at google.com>, Validation List <validation at cabforum.org>, Niko Carpenter <NCarpenter at securetrust.com>
Subject: RE: [cabf_validation] Clarifying Acceptable Status Codes for Following Redirects in methods 18 and 19

Well, this isn’t a spring cleanup thing.  Though it would be a good ballot.  I’d be more than happy to support getting rid of 300; getting down to an explicit list of codes whose semantics we have analyzed and approved would be even better.  

Thanks for starting the discussion, Niko.

-Tim

From: Validation <validation-bounces at cabforum.org> On Behalf Of Ryan Sleevi via Validation
Sent: Friday, April 24, 2020 2:57 PM
To: Niko Carpenter <NCarpenter at securetrust.com>
Cc: CABforum3 <validation at cabforum.org>
Subject: Re: [cabf_validation] Clarifying Acceptable Status Codes for Following Redirects in methods 18 and 19

I don't disagree that it'd be a normative change, for sure. But adding the entire IANA registry is sort of like the "any other method", and much of the discussion in the validation WG was about concerns of using content-aware redirects (which, functionally, 300 is, as it's dependent upon the UA/client understanding the media type)

Definitely, more feedback from more CAs would be good here. For example, 303 is not entirely unreasonable, but I think it'd have to be coupled with a more normative protocol descriptor ala ACME to evaluate.

And with 308, we have to make sure the client actually understands 308 semantics, so that it doesn't fall back into a 300-style content-aware parse (for which the canonical example is a meta-refresh, which folks understandably wanted to prohibit)

On Fri, Apr 24, 2020 at 2:50 PM Niko Carpenter <NCarpenter at securetrust.com> wrote:

I’m not opposed to restricting redirects to the 301, 302, 307, and 308 status codes. However, doing so would be a normative change, since 300 and 303 are not currently disallowed. Some Cas might already be following them, if they are relying on an HTTP client library to handle redirects in the manner described in RFC 7231, Section 6.4. 

Niko Carpenter 
Software Engineer

From: Ryan Sleevi <sleevi at google.com>
Date: Friday, April 24, 2020 at 12:10
To: Niko Carpenter <NCarpenter at securetrust.com>, Validation List <validation at cabforum.org>
Subject: Re: [cabf_validation] Clarifying Acceptable Status Codes for Following Redirects in methods 18 and 19

Right, that's why I proposed 301, 302, 307, and 308. The motivation for that is basically covered in RFC 7538 Section 1, and what you reach when you go through 7231: 305 / 306 are retired, and 300 requires parsing the body to semantically extract which choice.

On Fri, Apr 24, 2020 at 12:53 PM Niko Carpenter via Validation <validation at cabforum.org> wrote:

While I don’t think it’s worth calling out specifically in the BRs, CAs definitely should not be parsing response bodies to discern redirect URLs.

Niko Carpenter 
Software Engineer  

From: Ryan Sleevi <sleevi at google.com>
Date: Friday, April 24, 2020 at 10:49
To: Niko Carpenter <NCarpenter at securetrust.com>
Subject: Re: [cabf_validation] Clarifying Acceptable Status Codes for Following Redirects in methods 18 and 19

How do you propose CAs handle 300?

On Fri, Apr 24, 2020 at 11:44 AM Niko Carpenter <NCarpenter at securetrust.com> wrote:

I think it would be best to reference the IANA registry, so that we don’t need to draft a new ballot if a new status code is created. I propose replacing the following

> Redirects MUST be the result of an HTTP status code result within the 3xx Redirection class of status codes, as defined in RFC 7231, Section 6.4.

With

> Redirects MUST be the result of an HTTP status code result within the 3xx Redirection class of status codes, as registered in the IANA HTTP Status Code Registry.

Niko Carpenter 
Software Engineer  

From: Ryan Sleevi <sleevi at google.com>
Date: Thursday, April 23, 2020 at 12:02
To: Niko Carpenter <NCarpenter at securetrust.com>, Validation List <validation at cabforum.org>
Subject: Re: [cabf_validation] Clarifying Acceptable Status Codes for Following Redirects in methods 18 and 19

To clarify: The "intention" aspect is because the status codes in 6.4 are used to establish a new IANA registry (in Section 8.2 of RFC 7231), which RFC 7238, Section 6 then updates.

Did you mean to reference https://tools.ietf.org/html/rfc7538 though? That's updated (in both the IANA registry and in the IETF) as being the standards-track version of 308.

Are you thinking it's better to clarify that 301, 302, 307, and 308 are permitted, or to reference the IANA registry so that 300 and 303 are also permitted? 

On Thu, Apr 23, 2020 at 12:45 PM Niko Carpenter via Validation <validation at cabforum.org> wrote:

Methods 3.3.2.4.18 and 3.2.2.4.19, added in ballot SC25, say "Redirects MUST be the result of an HTTP status code result within the 3xx Redirection class of status codes, as defined in RFC 7231, Section 6.4." While I believe the intention was that following a 308 redirect should be acceptable, RFC 7231 does not define it.  Instead, it mentions, in section 6.4.7, that it is defined in RFC 7238. I think we should clarify that following a 308 redirect is acceptable in a new ballot, or the spring cleanup ballot.

Niko Carpenter

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