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 <
tors...@lodderstedt.net> 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.
> _______________________________________________
> OAuth mailing list
> OAuth@ietf.org
> https://www.ietf.org/mailman/listinfo/oauth
>
>
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