]> Axiomatics

Canada david.brossard@gmail.com

Rock Solid Knowledge

United Kingdom andy@rocksolidknowledge.com

University of Kent School of Computing

t.dimitrakos@kent.ac.uk

Security Web Authorization Protocol authorization abac rebac rbac access control xacml policy language 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 and replaces 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 (), - Attribute-based access control (), and - Relationship-based access control () About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the Web Authorization Protocol Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction While authentication has largely been solved and standardized (see and SAML as successful authentication standards), not as much can be said of authorization. One of the oldest and more mature standards is , 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.

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.

Conventions and Definitions 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 when, and only when, they appear in all capitals, as shown here.

Security Considerations TODO Security

IANA Considerations This document has no IANA actions.

References Normative References Axiomatics AB NIST NIST Axiomatics Axiomatics Axiomatics In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf. This specification replaces and obsoletes the OAuth 1.0 protocol described in RFC 5849. [STANDARDS-TRACK] NIST NIST NIST CA Technologies Styra

Acknowledgments 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.