| Internet-Draft | alfa-authz | October 2024 |
| Brossard, et al. | Expires 7 April 2025 | [Page] |
The Abbreviated Language for Authorization 2.0 is a constrained policy language aimed at solving fine-grained authorization challenges. This specification builds on top of [XACML] and replaces [ALFA] to provide a more complete and easier language to use.¶
Use cases for ALFA 2.0 include the ability to express: - Role-based access control ([RBAC]), - Attribute-based access control ([ABAC]), and - Relationship-based access control ([ReBAC])¶
This note is to be removed before publishing as an RFC.¶
The latest revision of this draft can be found at https://davidjbrossard.github.io/alfa-authorization-language/draft-brossard-alfa-authz.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-brossard-alfa-authz/.¶
Discussion of this document takes place on the Web Authorization Protocol Working Group mailing list (mailto:oauth@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/oauth/. Subscribe at https://www.ietf.org/mailman/listinfo/oauth/.¶
Source for this draft and an issue tracker can be found at https://github.com/davidjbrossard/alfa-authorization-language.¶
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While authentication has largely been solved and standardized (see [OAUTH] and SAML as successful authentication standards), not as much can be said of authorization. One of the oldest and more mature standards is [XACML], the eXtensible Access Control Markup Language established in 2001 under the helm of OASIS. The latest version, XACML 3.0, was released in 2013.¶
Since, there has been little innovation in the authorization space. Two standards emerged:¶
ALFA: Abbreviated Language for Authorization (ALFA) is a domain-specific language for a high-level description of XACML policies. It is designed with ease of use in mind, for use by XACML policy writers. ALFA provides the means to present domain specific information, such as attribute identifiers, in compact form and lays down the basic principle to compile policies expressed in ALFA into XACML 3.0 policies. ALFA does not bring new semantics to XACML. Anything that can be expressed in ALFA must be expressible in XACML. ALFA has been designed in such a way that lossless round-trip translations is possible.¶
OPA: Open Policy Agent is an open source, general-purpose policy engine that unifies policy enforcement across the stack. OPA provides a high-level declarative language that lets you specify policy as code and simple APIs to offload policy decision-making from your software. [OPA]¶
While OPA became part of CNCF, ALFA remained as a draft under OASIS. OPA's strength is also its drawback. It's a fullblown Datalog-based programming language which can achieve anything: it's extremely broad. As for ALFA, as mentioned above, it's true to XACML and aims to achieve lossless round-trip translations leading to unnecessary complications in ALFA's existing grammar.¶
The aim of this standard is to provide a simple and constrained authorization language largely inspired by ALFA but not tied to XACML and not limited by the need to provide round-tripping.¶
The model put forth by this specification follows the same approach as OASIS ALFA 1.0 [ALFA] and OASIS XACML 3.0 [XACML]. It departs from both these languages by being more lightweight and simpler. ALFA 2.0 can be used in a broader set of environments especially internet protocols and devices, constrained environments and is developer-friendly, i.e. it can be written by hand.¶
One of the goals of ALFA 2.0 is also to become more relevant to existing standards such as:¶
This profile purposely does not define a request/response protocol. Both the JSON Profile of XACML and the Authorization API 1.0 – draft 01 of Open ID may be used to send an authorization request and produce a decision.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
TODO Security¶
This document has no IANA actions.¶
The authors would like to acknowledge the authors of the original version of ALFA namely Pablo Giambiagi and Dr. Srijith Nair. The authors would also like to acknowledge Erik Rissanen, the then editor of the XACML Technical Committee.¶