[OAUTH-WG] Comments on OAuth 2.0 Rich Authorization Requests (draft-ietf-oauth-rar-01)
Denis <denis.ietf@free.fr> Wed, 27 May 2020 17:17 UTC
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From: Denis <denis.ietf@free.fr>
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Date: Wed, 27 May 2020 19:17:03 +0200
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Subject: [OAUTH-WG] Comments on OAuth 2.0 Rich Authorization Requests (draft-ietf-oauth-rar-01)
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This document states that the "scope" parameter used to specify the requested scope of an access token is only "sufficient to implement static scenarios and coarse-grained authorization requests". The intent of this draft is to specify "fine-grained authorization requirements", such as "please let me make a payment with the amount of 45 Euros" or "please give me read access to folder A and write access to file X". The proposed draft presents some similarities with a capability model where the holder of an access token is given the right by an AS to perform some operation(s) on an object through the content of the access token. Such an approach has privacy issues which are currently not documented in the Privacy Considerations section. The AS would be in a position to know, not only which resources servers are going to be accessed, but also what kind of operations are going to be performed by its clients on the resource servers. With such an approach, ASs will have the knowledge of every operation that is likely to be performed by a user on every RS. As a consequence, the AS would also be in a position to trace the actions performed by its users on the resources servers with which it has a relationship. Other approaches allowingto specify "fine-grained authorization requirements", that are more "privacy friendly" should be considered to address the initial problem. ADDITIONAL ARCHITECTURAL COMMENT OAuth initially assumed a static relationship between clients, authorization servers and resource servers. The original model for OAuth was making the assumption that the AS and the RS had a strong bilateral relationship. A key question is whether such strong relationship will be maintained for ever or whether it will be allowed to perform some evolutions of this relationship. In order to respect the privacy of the users, there is the need to encompass other scenarios. One of these scenarios is that the AS and the RS do not need any longer to have such a strong relationship. In terms of trust relationships, a RS simply needs to trust the access tokens issued by an AS. The AS does have any more a "need to know" of all the RSs that are accepting its access tokens. This would be a major simplification of the current global architecture. oauth-security-topics states: The privileges associated with an access token SHOULD be restricted to the minimum required for the particular application or use case. This means that the client should be able to select by itself the claims it would like to be placed into an access token with respect to the operations it is willing to perform on a RS. As long as only the scope request parameter will be usable in an access token request to select the claims to be placed into an access token, it will not be possible to remove this strong relationship. Denis