Re: [OAUTH-WG] Dynamic Scopes

[George Fletcher <[e-mail]>]

I like the concept of parameterized scopes but I'm not sure they should 
be used for per-transaction use cases. It seems like the use cases 
presented are about operating on parameters specific to the transaction. 
Why are these part of the authorization flow?

Is the goal to bind an access token to a particular transaction? If this 
is the case, would it not be better to either extend the refresh_token 
flow or may better yet, create a new grant_type that takes the 
refresh_token and additional "binding" parameters and then have that 
return the "bound" access token to be used for the transaction.

Maybe this is similar to what Nat is describing with the staging API?

Thanks,
George

On 6/20/18 5:58 PM, Brian Campbell wrote:
> In my own personal and humble opinion, Torsten, what you describe as 
> "(1) Parameter is part of the scope value" is the most natural 
> approach and works without needing changes to, or going outside of, 
> RFC6749 The OAuth 2.0 Authorization Framework. There may be AS 
> implementations that have made assumption about scope values being 
> static (I know of at least one!) but that's an implementation/feature 
> issue, which can change, and not a spec issue.
>
> The OIDC "claims" parameter is already a bit of a hairy beast and I 
> think using it and the ID Token to convey more dynamic 
> access/authorization is blurring the line between authorization and 
> authentication a bit much. Also, as others have pointed out, OIDC 
> isn't always in play - particularly for regular old authorization cases.
>
> An additional query parameter might be simple for a one-off case but 
> it's nonstandard and not very repeatable.
>
>
> On Mon, Jun 18, 2018 at 9:34 AM, Torsten Lodderstedt 
> <[e-mail] <mailto:[e-mail]>> wrote:
>
>     Hi all,
>
>     I have been working lately on use cases where OAuth is used to
>     authorize transactions in the financial sector and electronic
>     signing. What I learned is there is always the need to pass
>     resource ids (e.g. account numbers) or transaction-specific values
>     (e.g. amount or hash to be signed) to the OAuth authorization
>     process to further qualify the scope of the requested access token.
>
>     It is obvious a static scope value, such as „payment“or „sign“,
>     won’t do the job. For example in case of electronic signing, one
>     must bind the authorization/access token to a particular document,
>     typically represented by its hash.
>
>     I would like to get your feedback on what you consider a good
>     practice to cope with that challenge. As a starting point for a
>     discussion, I have assembled a list of patterns I have seen in the
>     wild (feel free to extend).
>
>     (1) Parameter is part of the scope value, e.g.
>     „sign:<hash_to_be_signed>“ or "payments:<payment_resource_id>" - I
>     think this is an obvious way to represent such parameters in
>     OAuth, as it extends the scope parameter, which is intended to
>     represent the requested scope of an access token. I used this
>     pattern in the OAuth SCA mode in Berlin Group's PSD API.
>
>     (2) One could also use additional query parameter to add further
>     details re the requested authorization, e.g.
>
>     GET /authorize?
>     .....
>     &scope=sign
>     .....
>     &hash_to_be_signed=<hash_to_be_signed>
>
>     It seems to be robust (easier to implement?) but means the scope
>     only represents the static part of the action. The AS needs to
>     look into a further parameter to fully understand the requested
>     authorization.
>
>     (3) Open Banking UK utilizes the (OpenID Connect) „claims“
>     parameter to carry additional data.
>
>     Example:
>
>     "claims": {
>         "id_token": {
>             "acr": {
>                 "essential": true,
>                 "value": "..."
>               },
>             "hash_to_be_signed": {
>                 "essential": true,
>                 "value": "<hash_to_be_signed>"
>             }
>         },
>         "userinfo": {
>             "hash_to_be_signed": {
>                 "essential": true,
>                 "value": "<hash_to_be_signed>"
>             }
>         }
>       }
>
>     I‘m looking forward for your feedback. Please also indicated
>     whether you think we should flush out a BCP on that topic.
>
>     kind regards,
>     Torsten.
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