Re: [Acme] Specify which JWS serialization is used

[Martin Thomson <[e-mail]>]

415 is for the case where a client provides bad request content, so yes.
See rfc7694 for details.

 406 is for failed conneg. Not something you expect to see much here.

On 5 Mar. 2018 09:25, "Richard Barnes" <[e-mail]> wrote:

The lengths of the emails in this thread illustrate the complexity risk
here :)

In the interest of simplicity, I would really like to stick to Flattened
JSON unless someone has **strong** objections.

Logan, to your point about library compatibility, two notes: (1) it's OK if
we front-run libraries a little.  It's not hard for libraries to upgrade;
this is only formatting, no crypto changes needed.  (2) Empirically, this
must not be too big a blocker for people, since as Jacob notes, Let's
Encrypt only supports Flattened JSON right now and they've got a bunch of
clients talking to them.

As far as headers / response codes: You're correct that 406 is wrong / 415
is right.  But ISTM that Accept is still the right header to say what is
right.  So the server should return 415+Accept.  Copying Thomson to check
our work here.

--Richard

On Sun, Mar 4, 2018 at 10:43 AM, Logan Widick <[e-mail]>
wrote:

> How about this: Specify a default format (either "application/jose" for
> Compact Serialization, or "application/jose+json" with Flattened
> Serialization - I have no preference which one), with optional support for
> other formats if needed? Even with JOSE libraries that don't support all
> serializations and/or don't provide control over which serialization is
> used, a programmer would at least need to know (or experimentally find out)
> if a JSON serialization or if the compact one is being produced. If a JSON
> serialization is selected as the default, a programmer should be able to
> convert between the two JSON serializations easily as needed before and/or
> after using a JOSE library. If a JSON format is declared as the default but
> the JOSE library only has the compact one, or vice-versa, conversion before
> and/or after the JOSE library would be more complex but should still be
> doable with guidance.
>
> The directory meta item could be defined as something like:
>
>    - supportedSerializations: An array of supported serialization formats
>    as described in {{jws-serialization-formats}}. If this is not specified,
>    assume that the server only supports [insert selected default here].
>
> Then, the JWS Serialization Formats section could be changed to something
> like the following:
>
> The JSON Web Signature (JWS) specification {{!RFC7515}} contains multiple
> JWS serialization formats. When sending an ACME request with a non-empty
> body, an ACME client implementation SHOULD use the HTTP Content-Type
> {{!RFC7231}} header to indicate which JWS serialization format is used for
> encapsulating the ACME request payload.
>
> Each serialization format defined for use in ACME is described with a
> content type, and a series of ACME-specific restrictions on root JWS and
> nested JWS instances.  A "root JWS" is a JWS used to encapsulate an entire
> ACME request payload, and a "nested JWS" is a JWS contained within the ACME
> request payload (such as the "externalAccountBinding" described in
> {{external-account-binding}} or the "key-change" object described in
> {{account-key-roll-over}}). Below are the JWS serialization formats that
> are defined for use in ACME:
>
> [same list as before but with the default format coming first]
>
> If no Content-Type is provided, the default serialization type is [insert
> selected default here]. Servers MUST support [insert selected default
> here]. [NOTE: If a JSON format is selected as the default, say that a
> server SHOULD support the other JSON format.] A server MAY support
> additional serializations, such as [insert serialization(s) not picked
> here], by including a "supportedSerializations" field in the directory
> "meta" object as described in {{directory}}.
>
> If a server receives a request using a serialization it does not support,
> the server MUST send a response with HTTP status code 415 (Unacceptable
> Media Type) and a problem document with error type
> "unsupportedSerialization". This problem document SHOULD contain a
> "supportedSerializations" array of strings indicating the acceptable
> serialization content types.
>
> [TODO: If a client uses the General JSON Serialization but it turns out
> the server only supports the Flattened JSON Serialization (or vice-versa),
> explain that a 415 response indicates that the client will need to switch
> JSON formats]
>
> [TODO: Insert a sentence or two specifying what happens if a supported
> serialization is used but the serialization is malformed? Should this be
> 400 Bad Request + malformed error code + supportedSerializations?]
>
> In the examples below, JWS objects are shown in the Flattened JSON
> serialization, with the protected header and payload expressed as
> base64url(content) instead of the actual base64-encoded value, so that the
> content is readable. [Example readability is a very high priority
> regardless of which serialization format is actually chosen as the default,
> and the current convention of Flattened JSON + base64url(content) is about
> as readable as it gets, so I don't think any changes will need to be made
> here]
>
>
> On Sun, Mar 4, 2018 at 8:33 AM, Jörn Heissler <
> [e-mail]> wrote:
>
>> On Sun, Mar 04, 2018 at 07:45:36 -0600, Logan Widick wrote:
>> > Good catch. Should it be 415 (Unsupported Media Type) plus which of the
>> > following (or which combination of the following):
>> >
>> >    - A new problem document field (tentatively named
>> >    "supportedSerializations": an array of media type strings)?
>> >    - A new directory field (tentatively named
>> "supportedSerializations": an
>> >    array of media type strings)?
>> >       - Should this go in the directory's "meta" object, or in the
>> >       directory object itself?
>> >    - A HTTP header?
>> >    - Something else?
>>
>> I like the directory approach with meta. Then a client could
>> use this information before sending the first POST. Else the client
>> would need to change an internal state after receiving the error
>> message. For my own client, I'm planning to support the OpenPGP smart
>> card. It takes 3 seconds to generate a signature. If a signature is
>> wasted to find out that the default serialization is not supported, it
>> would be annoying. Having to write a configuration file "use compact by
>> default for CA foo" would be stupid too.
>>
>> This, and the problem document field. "supportedSerializations" sounds
>> fine.
>>
>> Should the two features be OPTIONAL?
>>
>> I don't like HTTP headers, it's quite complicated to parse them correctly.
>> JSON is so much easier.
>>
>>
>> Or... specify that flattened MUST BE used :-)
>>
>> Cheers
>> Joern Heissler
>>
>
>