Re: [Txauth] A model with a User Consent Element (with a clean figure)

[Denis <[e-mail]>]

Hi Dick,

> Hi Denis, thanks for sharing the model. I don't fully understand what 
> is going on, questions inserted:
Responses are inserted.
>
> FWIW: having paragraphs start with the step number (1), (2) etc. would 
> make it easier to map between the description and the diagram.
>
> On Thu, Jul 9, 2020 at 3:26 AM Denis <[e-mail] 
> <mailto:[e-mail]>> wrote:
>
>     This is a new thread.
>
>     Preamble: This model is quite different from the XAuth model.
>     In particular, a RO has no relationship with any AS and a Client
>     does not need to be associated with any AS prior to any access to
>     a RS.
>
>     A key point of this model is that the user's consent is handled
>     locally by the Client and hence no AS nor RS is handling a man
>     machine interface
>     for the user consent. This allows to support locally the user
>     consent for multiple ASs while keeping all ASs ignorant about the
>     choices of the user
>     made for accessing a particular RS.
>     *
>
>     **+--------++------------+
>     |User||Resource|
>     ||| Owner (RO) |
>     +--------++------------+
>     |\|
>     |\|
>     |\|
>     |\|
>     +-----------++---------------++------------+
>     ||---->| Authorization |||
>     || (2) |Server (AS)|||
>     ||<----||||
>     |Client|+---------------+||
>     ||-------------------------->|Resource|
>     |User|(1)|Server|
>     |Consent|<--------------------------|(RS)|
>     |element|||
>     ||-------------------------->||------>
>     ||(3)||(4)
>     ||<--------------------------||<------
>     +-----------++------------+
>     *
>     The flow of operations is as follows:
>
>     The Client (which may have been previously authenticated using FIDO)
>
> Which party has the client authenticated to? The client authenticating 
> with FIDO is confusing to me. FIDO is usually how a user authenticates.

If the user has previously opened a user account with the RS using FIDO, 
then the client may be authenticated by the RS using FIDO.
In such a case, the user is already known to the RS under a pseudonym 
specific to the RS. It may (or may not) have previously presented access 
tokens
to that RS.

> contacts the RS and after some dialogue with the RS selects an operation
> How does the client know which RS to contact?

For a private usage, the user may use DuckDuckGo, while for business he 
may use an application from his company which lists various services
available in the context of his job or his position. Some services may 
be freely available to all the employees of the company with any 
authentication,
e.g. the phone book of the employees may be freely available on the 
intranet of the company, while some other services may require the user
to authenticate to the AS from the company.

> that it wants to perform on the RS (1a). Note that it may also 
> indicate directly the operation that it wants to perform on the RS 
> without any prior dialogue.
>
>     In return (1b), the RS informs the Client about which attributes
>     are needed by the RS for performing the requested operation and
>     from which Attributes Servers
>     they may be obtained.
>
> (1a) and (1b) are not labeled. There is only (1)

(1a) is the first exchange for (1) with the arrow from left to right, 
while (1b) is the response with the arrow from right to left.
The same applies to the other exchanges i.e. (2) , (3) and (4).

>
>     This information is specifically marked to indicate that it shall
>     be handled by the "User Consent element" from the Client.
>
> Why? What is the significance of this? Which information is marked?

In the response, a specific identifier or a magic number is used to 
indicate the start and the length of the information block
to be sent to the "User Consent element" supported by the Client.

> The presentation of that information is up to the man machine 
> interface supported by the "User Consent element" from the Client.
>
>
> Which information?

The attributes that are needed by the RS for performing a requested 
operation and from which Attributes Servers they may be obtained.

>
>     The user can see which attributes are requested by the RS for
>     performing the requested operation and, if it consents, the Client
>     contacts one or more
>     appropriate Authorization Servers (2a).
>
> How does the client know which AS(s) to contact?

For each AS trusted by the RS to perfom a given operation, the RS should 
indicate a user-friendly name and a URL of the AS.

>     The user consent is hence captured locally by the Client (i.e.
>     there is no dialogue with any AS nor any RS).
>
>
> No dialogue with who? The client is calling the AS is it not?

For the user consent, there is no external call since it is handled 
locally. Afterwards, there is a call to the AS(s) selected by the user.

>
>     When the Client got the access tokens from these authorization
>     servers (2b), it sends all of them in a single request to the RS (3a).
>
>
> So the RS must trust the AS that issued the tokens. And the AS must 
> trust the Client to have gathered consent.
Theses two assertions are correct.
> And the AS must have a relationship with the user.

Only when the user chooses one AS while giving its consent, then the 
user must have a relationship with the selected AS.

> It is unclear what role the RO is playing in this though. The RO and 
> RS look to be the same entity from all the other parties.

A RO, as indicated on the figure, has only a relationship with one RS: 
it has no relationship with any AS.
The RS trusts the AS but the AS does not know which RSs are trusting it.

>
> From my current understanding, at a high level, this looks like it is 
> supported by GNAP with the addition of the discovery step (1).

Well, it is fairly different :

    1) The first major difference is that there is no arrow between the
    RO and the AS. No protocol or "out-of-bands" means are necessary.

    2) The second major difference is that there is no arrow between the
    AS and the RS. No protocol is necessary.

    3) The third major difference is that the AS does not know any RS.
    Note: for backward compatibility reasons, an exception might exist
    for "old" Auth 2.0 ASs.

    4) The fourth major difference is that the XAuth spec. is rather
    vague to describe when and by who the user consent is captured:
         XAuth states on page 4: "User consent is /often /required at
    the GS". In that case, the GS is able to act as Big Brother. No
    other case is described.

    5) The fifth major difference is that the data that is transferred
    to a "User Consent Element" to capture the user consent. That data
    can be standardized.
         Moreover, it will also be possible to standardize the dialogue
    between the RO and the RS. The RO will then be able to manage
    remotely the authorization tables.
         See my email sent on June 6, with the following subject:
    "Support of FIDO and data minimization by RSs".

    6) Another difference is the following: since there is no
    interaction between the RO and the AS, "authorizations from the RO"
    as described in XAuth do not exist. 

> There have been a number of proposals for doing this discovery, and 
> perhaps now there are enough use cases to look at standardizing 
> something.
> No interaction is needed between the AS and the User as the Client is 
> providing enough "information" in the user object of the Grant Request
> to satisfy the AS releasing the access tokens.
Not sure I understand correctly this last sentence.
>
> Perhaps as I understand the model in more detail I will understand 
> what is missing from GNAP (besides the discovery step).

It would be hard to say "what is missing" from XAuth since the 
foundations are not the same.

In order to compare different architectures, there is the need to start 
with the trust relationships.
Unfortunately, the word "trust" is absent in the main body of 
draft-hardt-xauth-protocol-12. Hence,
the description of the trust relationships is missing.

Denis

>
> /Dick
>
> (I've skipped reviewing the delegation use case below until I 
> understand the simple use case)
>
>
>     End of the story for a simple access
>
>
>     Start of a subsequent story for a delegation case
>
>     Let us now suppose that the RS is unable to fulfil the request by
>     its own and that it needs to contact another RS. RS1 contacts RS2
>     (4a) and indicates the operation
>     that it wants to perform on RS2 (that operation may not be the
>     same as the original operation). In return (4b), RS2 informs RS1
>     about which attributes are needed
>     by RS2 for performing the requested operation and from which
>     Attributes Servers they may be obtained. RS1 forwards that
>     information to the Client.
>
>     This information is marked to indicate that it shall be handled by
>     the "User Consent element" from the Client. The presentation of
>     that information is up to the man machine
>     interface from the Client. The user can see which attributes are
>     requested by RS2 for performing the new requested operation and,
>     if it consents, the Client contacts one or more
>     appropriate Authorization Servers. The user consent is hence
>     captured locally by the "User Consent element" from the Client.
>     (i.e. there is no dialogue with any AS, nor RS1, nor RS2).
>
>     When the Client got the access token(s) from the authorization
>     server(s), it sends all of them in a single request to RS1. RS1
>     then forwards the additional access token(s) to RS2.
>
>
>     Some observations:
>
>     The user nor the Client are linked with any particular AS. A user
>     may use today an AS of the Bank of America and may change tomorrow
>     to the Bank of Missouri.
>     As soon as he will be registered with the Bank of Missouri, he
>     will be able to get access tokens from the AS of the Bank of
>     Missouri. The AS of Bank of America
>     has not been able to know where its access tokens have been used.
>     This will be the same for AS of the Bank of Missouri. There is no
>     need for any direct dialogue
>     between any AS and any RS at the time a client is making an
>     access. There is no need for any RO to contact any AS.
>
>     This model has been constructed following a "Privacy by Design"
>     approach.
>
>     Denis
>
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> ᐧ