From Access Control to Usage Control with User-Managed Access

Wout Slabbinck, Ruben Dedecker, Beatriz Esteves

Keywords: Usage Control, Solid, user managed access

Abstract:

Solid leverages Semantic Web technologies to enable interoperable storage, access and (re)use
of resources within a decentralized global ecosystem [1 ]. Originating from before the dawn
of modern access control —when Authorization header schemes were the most elaborate
mechanism available for HTTP— the project came up with WAC [ 2] and ACP [ 3 ], languages for
writing policy lists, with an algorithm for evaluating those. Around the same time —in the early
2000s— enough developers started bumping into the limits the HTTP Authorization header
(as well as initial proprietary lock-in ’solutions’) to spark the creation of OAuth [ 4], today’s de
facto standard for access control on the Web. However, just like authorization was an explicit
non-goal in HTTP, OAuth did not provide authentication as a service. This was later remedied
by the OpenID initiative, which constructed an identity layer on top of it in the form of OpenID
Connect [5].
While the Solid project incorporated aspects of both OAuth and OIDC in their specifications,
it has missed some key elements that make those standards so widely adopted. Both WAC
and ACP lack a separation of concerns between resource servers and authorization servers,
leading to a request-efficient but inflexible system. By synchronously evaluating access controls
based on a resource request and accompanying authentication token over the policy documents
stored in the resource hierarchy of the Solid pod, the ability to request and evaluate claims
—outside webid, identity provider and client provided by the authentication token— is restricted.
Access control management is tailored to the specific interface(s) (protection domain) of a single
resource server, and therefore impractical to manage and audit over multiple servers. The choice
of policy language, evaluation algorithm, and authentication options are tightly bound to the
evolution of that specific resource server, to which authentication details are unnecessarily
revealed. Moreover, they rely on a hierarchical resource structure, which assumes a read-write
symmetry, and prevents full independence of data and application, leading to a proliferation of
non-interoperable application-specific APIs on top of Solid.

We implemented an open-source UMA prototype governing
usage control to Solid servers through integration with the Community Solid Server (CSS): https://github.com/SolidLabResearch/user-managed-access/ .

Submission Number: 5