[secdir] SECDIR review of draft-ietf-httpbis-p7-auth-24

[Stephen Kent <[e-mail]>]

I reviewed this document as part of the security directorate's ongoing 
effort to review all IETF documents being processed by the IESG.These 
comments were written primarily for the benefit of the security area 
directors.Document editors, WG chairs and ADs should treat these 
comments just like any other last call comments.

The document obsoletes RFC 2616 and updates 2617. It says that it 
"defines HTTP/1.1 access control and authentication." I have not been 
tracking httpbis closely enough to know the specific motivations for 
generating this doc, so my review is unbiased by that context.

I see that "ought" is used in two places on page 6, but not in uppercase 
as per RFC 6919. The authors should revisit the use of this term here.

Also on page 6 it appears that the phrase "receipt of" was omitted in 
two places:

Upon *<> *a request for a protected resource that omits credentials

Likewise, upon *<>* a request that requires authentication by proxies

Later on page 6 the text says:

The HTTP protocol does not restrict applications to this simple

challenge-response framework for access authentication.Additional

mechanisms MAY be used, such as encryption at the transport level or

via message encapsulation, and with additional header fields

specifying authentication information.However, such additional

mechanisms are not defined by this specification.

Encryption is not, per se, an authentication mechanism. Please revise 
this text.

In Section 2.2 the text says:

The protection space determines the domain over which credentials can

be automatically applied.If a prior request has been authorized,

the user agent MAY reuse the same credentials for all other requests

within that protection space for a period of time determined by the

authentication scheme, parameters, and/or user preference.

I'm not clear how user preferences fit into this process. It would seem 
that the server would decide whether a prior authorization is valid for 
later requests, not a user.

The end of Section 2.2 includes the word "might" but not uppercase, as 
per RFC 6919. I again suggest that the authors reconsider using this 
term in this context.

In Section 4.3, the text says:

A proxy MAY relay

the credentials from the client request to the next proxy if that is

the mechanism by which the proxies cooperatively authenticate a given

request.

If, as stated here, a set of proxies cooperatively authenticate a 
request, then isn't this a MUST vs. a MAY?

In Section 4.4 the text says:

Note: The challenge grammar production uses the list syntax as

well.Therefore, a sequence of comma, whitespace, and comma can

be considered both as applying to the preceding challenge, or to

be an empty entry in the list of challenges.In practice, this

ambiguity does not affect the semantics of the header field value

Should "both" be "either" in the above text? Does the potentially 
ambiguous construct ever take on both meanings simultaneously?

Section 5.1.2 uses "ought" when discussing definitions for new 
authentication schemes. See comments above re use of this term.The same 
section also uses the phrase "need to" twice, where MUST seems appropriate.

The Security Considerations section (6) is about one page in length. It 
references the SC sections in two in I-Ds: 
draft-ietf-httpbis-p1-messaging-24 and 
draft-ietf-httpbis-p2-semantics-24. Both of these I-Ds have non-trivial 
SC sections, but one cannot say that this document has an acceptable SC 
section until those documents are finalized. They are both normative 
references, so this doc will nor progress independently, but there will 
still be a need to revisit this SC when those SCs are finalized.

The SC section here addresses only two issues: purging credentials in 
clients and user agents, and protection spaces. The discussion of the 
former topic does not discuss how credential purging applies to proxies. 
Also, it is not clear that a user control for credential purging will 
have the desired effect given a potentially complex GUI environment. The 
discussion of protection spaces provides useful suggestions on how to 
minimize credential exposure.

I was a bit surprised that there was no advice deprecating the use of 
passwords as credentials, if only to make a statement on this topic.