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Internet ACE Working Group Internet-Draft Information about which entities are authorized to perform what operations on which constituents of other entities is a crucial component of producing an overall system that is secure. Conveying precise authorization information is especially critical in highly automated systems with large numbers of entities, such as the "Internet of Things". This specification provides a generic information model and format for representing such authorization information, as well as two variants of a specific instantiation of that format for use with REST resources identified by URI path. About This Document Status information for this document may be found at . Discussion of this document takes place on the Authentication and Authorization for Constrained Environments (ace) Working Group mailing list (), which is archived at . Source for this draft and an issue tracker can be found at .

Introduction Constrained Devices as they are used in the "Internet of Things" need security in order to operate correctly and prevent misuse. One important element of this security is that devices in the Internet of Things need to be able to decide which operations requested of them should be considered authorized, need to ascertain that the authorization to request the operation does apply to the actual requester as authenticated, and need to ascertain that other devices they make requests of are the ones they intended. To transfer detailed authorization information from an authorization manager (such as an ACE-OAuth Authorization Server ) to a device, a compact representation format is needed. This document defines such a format, the Authorization Information Format (AIF). AIF is defined both as a general structure that can be used for many different applications and as a specific instantiation tailored to REST resources and the permissions on them, including some provision for dynamically created resources.

Terminology This memo uses terms from and ; CoAP is used for the explanatory examples as it is a good fit for Constrained Devices. The shape of data is specified in CDDL . Terminology for Constrained Devices is defined in . 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. The term "byte", abbreviated by "B", is used in its now customary sense as a synonym for "octet".

Information Model Authorizations are generally expressed through some data structures that are cryptographically secured (or transmitted in a secure way). This section discusses the information model underlying the payload of that data (as opposed to the cryptographic armor around it). For the purposes of this specification, the underlying access control model will be that of an access matrix, which gives a set of permissions for each possible combination of a subject and an object. We are focusing the AIF data item on a single row in the access matrix (such a row traditionally is also called a capability list), without concern to the subject for which the data item is issued. As a consequence, AIF MUST be used in a way that the subject of the authorizations is unambiguously identified (e.g., as part of the armor around it). The generic model of such a capability list is a list of pairs of object identifiers and the permissions the subject has on the object(s) identified.

Definition of Generic AIF = [* [Toid, Tperm]] ]]>

In a specific data model (such as the one also specified in this document), the object identifier (Toid) will often be a text string, and the set of permissions (Tperm) will be represented by a bitset in turn represented as a number (see ).

Commonly used shape of a specific AIF ]]>

REST-specific Model In the specific instantiation of the REST resources and the permissions on them, for the object identifiers (Toid), we use the URI of a resource on a CoAP server. More specifically, since the parts of the URI that identify the server ("authority" in ) are what are authenticated during REST resource access ( and ), they naturally fall into the realm handled by the cryptographic armor); we therefore focus on the "path" ("path-abempty") and "query" parts of the URI (URI "local-part" in this specification, as expressed by the Uri-Path and Uri-Query options in CoAP). As a consequence, AIF MUST be used in a way that it is clear who is the target (enforcement point) of these authorizations (note that there may be more than one target that the same authorization applies to, e.g., in a situation with homogeneous devices). For the permissions (Tperm), we use a simple permissions model that lists the subset of the REST (CoAP or HTTP) methods permitted. This model is summarized in . An authorization instance in the AIF Information Model

local-part	Permission Set
/s/temp	GET
/a/led	PUT, GET
/dtls	POST

In this example, a device offers a temperature sensor /s/temp for read-only access, a LED actuator /a/led for read/write, and a /dtls resource for POST access. As will be seen in the data model (), the representations of REST methods provided are limited to those that have a CoAP method number assigned; an extension to the model may be necessary to represent permissions for exotic HTTP methods.

Limitations This simple information model only allows granting permissions for statically identifiable objects, e.g., URIs for the REST-specific instantiation. One might be tempted to extend the model towards URI templates (for instance, to open up an authorization for many parameter values as in /s/temp{?any*}), however, that requires some considerations of the ease and unambiguity of matching a given URI against a set of templates in an AIF object. This simple information model also does not allow further conditionalizing access based on state outside the identification of objects (e.g., "opening a door is allowed if that is not locked"). Finally, the model does not provide any special access for a set of resources that are specific to a subject, e.g., that the subject created itself by previous operations (PUT, POST, or PATCH/iPATCH ) or that were specifically created for the subject by others.

REST-specific Model With Dynamic Resource Creation The REST-specific Model With Dynamic Resource Creation addresses the need to provide defined access to dynamic resources that were created by the subject itself, specifically, a resource that is made known to the subject by providing Location-* options in a CoAP response or using the Location header field in HTTP (the Location-indicating mechanisms). (The concept is somewhat comparable to "ACL inheritance" in NFSv4 , except that it does not use a containment relationship but the fact that the dynamic resource was created from a resource to which the subject had access.) In other words, it addresses an important subset of the third limitation mentioned in . An authorization instance in the AIF Information Model

local-part	Permission Set
/a/make-coffee	POST, Dynamic-GET, Dynamic-DELETE

For a method X, the presence of a Dynamic-X permission means that the subject holds permission to exercise the method X on resources that have been returned in a 2.01 (201) response by a Location-indicating mechanism to a request that the subject made to the resource listed (/a/make-coffee in the example shown in , which might return the location of a resource that allows GET to find out about the status and DELETE to cancel the coffee-making operation). Since the use of the extension defined in this section can be detected by the mentioning of the Dynamic-X permissions, there is no need for another explicit switch between the basic and the model extended by dynamic resource creation; the extended model is always presumed once a Dynamic-X permission is present.

Data Model Different data model specializations can be defined for the generic information model given above. In this section, we will give the data model for simple REST authorization as per and . As discussed, in this case the object identifier is specialized as a text string giving a relative URI (local-part as absolute path on the server serving as enforcement point). The permission set is specialized to a single number by the following steps:

• The entries in the table that specify the same local-part are merged into a single entry that specifies the union of the permission sets.
• The (non-dynamic) methods in the permission sets are converted into their CoAP method numbers, minus 1.
• Dynamic-X permissions are converted into what the number would have been for X, plus a Dynamic-Offset chosen as 32 (e.g., 35 for Dynamic-DELETE).
• The set of numbers is converted into a single number by taking each number to the power of two and computing the inclusive OR of the binary representations of all the power values.

This data model could be interchanged in the JSON representation given in .

An authorization instance encoded in JSON (40 bytes)

In , a straightforward specification of the data model (including both the methods from and the new ones from , identified by the method code minus 1) is shown in CDDL :

AIF in CDDL path = tstr ; URI relative to enforcement point permissions = uint .bits methods methods = &( GET: 0 POST: 1 PUT: 2 DELETE: 3 FETCH: 4 PATCH: 5 iPATCH: 6 Dynamic-GET: 32; 0 .plus Dynamic-Offset Dynamic-POST: 33; 1 .plus Dynamic-Offset Dynamic-PUT: 34; 2 .plus Dynamic-Offset Dynamic-DELETE: 35; 3 .plus Dynamic-Offset Dynamic-FETCH: 36; 4 .plus Dynamic-Offset Dynamic-PATCH: 37; 5 .plus Dynamic-Offset Dynamic-iPATCH: 38; 6 .plus Dynamic-Offset ) ]]>

For the information shown in and , a representation in CBOR is given in ; again, several optimizations/improvements are possible.

An authorization instance encoded in CBOR (28 bytes)

Note that choosing 32 as Dynamic-Offset means that all future CoAP methods that can be registered can be represented both as themselves and in the Dynamic-X variant, but only the dynamic forms of methods 1 to 21 are typically usable in a JSON form .

Media Types This specification defines media types for the generic information model, expressed in JSON (application/aif+json) or in CBOR (application/aif+cbor). These media types have parameters for specifying Toid and Tperm; default values are the values "local-uri" for Toid and "REST-method-set" for Tperm. A specification that wants to use Generic AIF with different Toid and/or Tperm is expected to request these as media type parameters () and register a corresponding Content-Format ().

IANA Considerations RFC Ed.: throughout this section, please replace RFC XXXX with the RFC number of this specification and remove this note.

Media Types IANA is requested to add the following Media-Types to the "Media Types" registry.

Name	Template	Reference
aif+cbor	application/aif+cbor	RFC XXXX,
aif+json	application/aif+json	RFC XXXX,

For application/aif+cbor:

Type name:

application

Subtype name:

aif+cbor

Required parameters:

none

Optional parameters:

• Toid: the identifier for the object for which permissions are supplied. A value from the media-type parameter sub-registry for Toid. Default value: "local-uri" (RFC XXXX).
• Tperm: the data type of a permission set for the object identified via a Toid. A value from the media-type parameter sub-registry for Tperm. Default value: "REST-method-set" (RFC XXXX).

Encoding considerations:

binary (CBOR)

Security considerations:

of RFC XXXX

Interoperability considerations:

none

Published specification:

of RFC XXXX

Applications that use this media type:

Applications that need to convey structured authorization data for identified resources, conveying sets of permissions.

Fragment identifier considerations:

The syntax and semantics of fragment identifiers is as specified for "application/cbor". (At publication of RFC XXXX, there is no fragment identification syntax defined for "application/cbor".)

Person & email address to contact for further information:

ACE WG mailing list (ace@ietf.org), or IETF Applications and Real-Time Area (art@ietf.org)

Intended usage:

COMMON

Restrictions on usage:

none

Author/Change controller:

IETF

Provisional registration:

no

For application/aif+json:

Type name:

application

Subtype name:

aif+json

Required parameters:

none

Optional parameters:

• Toid: the identifier for the object for which permissions are supplied. A value from the media-type parameter sub-registry for Toid. Default value: "local-uri" (RFC XXXX).
• Tperm: the data type of a permission set for the object identified via a Toid. A value from the media-type parameter sub-registry for Tperm. Default value: "REST-method-set" (RFC XXXX).

Encoding considerations:

binary (JSON is UTF-8-encoded text)

Security considerations:

of RFC XXXX

Interoperability considerations:

none

Published specification:

of RFC XXXX

Applications that use this media type:

Applications that need to convey structured authorization data for identified resources, conveying sets of permissions.

Fragment identifier considerations:

The syntax and semantics of fragment identifiers is as specified for "application/json". (At publication of RFC XXXX, there is no fragment identification syntax defined for "application/json".)

Person & email address to contact for further information:

ACE WG mailing list (ace@ietf.org), or IETF Applications and Real-Time Area (art@ietf.org)

Intended usage:

COMMON

Restrictions on usage:

none

Author/Change controller:

IETF

Provisional registration:

no

Registries IANA is requested to create a sub-registry for application/aif+cbor and application/aif+json within for the two media-type parameters Toid and Tperm, populated with:

Parameter	name	Description/Specification	Reference
Toid	local-part	local-part of URI	RFC XXXX
Tperm	REST-method-set	set of REST methods represented	RFC XXXX

The registration policy is Specification required . The designated expert will engage with the submitter to ascertain the requirements of this document are addressed.

Content-Format IANA is requested to register Content-Format numbers in the "CoAP Content-Formats" sub-registry, within the "Constrained RESTful Environments (CoRE) Parameters" Registry , as follows:

Media Type	Content Coding	ID	Reference
application/aif+cbor	-	TBD1	RFC XXXX
application/aif+json	-	TBD2	RFC XXXX

// RFC Ed.: please replace TBD1 and TBD2 with assigned IDs and remove this note. Note that applications that register Toid and Tperm values are encouraged to also register Content-Formats for the relevant combinations.

Security Considerations The security considerations of apply. Some wider issues are discussed in . The semantics of the authorization information defined in this documents are that of an allow-list: everything is denied until it is explicitly allowed. When applying these formats, the referencing specification needs to be careful to:

• ensure that the cryptographic armor employed around this format fulfills the referencing specification's security objectives, and that the armor or some additional information included in it with the AIF information (1) unambiguously identifies the subject to which the authorizations shall apply and provides (2) any context information needed to derive the identity of the object to which authorization is being granted from the object identifiers (such as, for the data models defined in the present specification, the scheme and authority information that is used to construct the full URI), and
• ensure that the types used for Toid and Tperm provide the appropriate granularity and precision so that application requirements on the precision of the authorization information are fulfilled, and that all parties understand Toid/Tperm pairs to signify the same operations.

For the data formats, the security considerations of and apply. A plain implementation of AIF might implement just the basic REST model as per . If it receives authorizations that include permissions that use the REST-specific Model With Dynamic Resource Creation , it needs to either reject the AIF data item entirely or act only on the permissions that it does understand. In other words, the semantics underlying an allow-list as discussed above need to hold here as well. An implementation of the REST-specific Model With Dynamic Resource Creation needs to carefully keep track of the dynamically created objects and the subjects to which the Dynamic-X permissions apply -- both on the server side to enforce the permissions and on the client side to know which permissions are available.

References Normative References A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK] The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation. CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments. Adobe Fastly greenbytes GmbH The Hypertext Transfer Protocol (HTTP) is a stateless application- level protocol for distributed, collaborative, hypertext information systems. This document describes the overall architecture of HTTP, establishes common terminology, and defines aspects of the protocol that are shared by all versions. In this definition are core protocol elements, extensibility mechanisms, and the "http" and "https" Uniform Resource Identifier (URI) schemes. This document updates RFC 3864 and obsoletes RFC 2818, RFC 7231, RFC 7232, RFC 7233, RFC 7235, RFC 7538, RFC 7615, RFC 7694, and portions of RFC 7230. Many protocols make use of points of extensibility that use constants to identify various protocol parameters. To ensure that the values in these fields do not have conflicting uses and to promote interoperability, their allocations are often coordinated by a central record keeper. For IETF protocols, that role is filled by the Internet Assigned Numbers Authority (IANA). To make assignments in a given registry prudently, guidance describing the conditions under which new values should be assigned, as well as when and how modifications to existing values can be made, is needed. This document defines a framework for the documentation of these guidelines by specification authors, in order to assure that the provided guidance for the IANA Considerations is clear and addresses the various issues that are likely in the operation of a registry. This is the third edition of this document; it obsoletes RFC 5226. This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. The Concise Data Definition Language (CDDL), standardized in RFC 8610, provides "control operators" as its main language extension point. The present document defines a number of control operators that were not yet ready at the time RFC 8610 was completed: , , and for the construction of constants; / for including ABNF (RFC 5234 and RFC 7405) in CDDL specifications; and for indicating the use of a non-basic feature in an instance. 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 This Glossary provides definitions, abbreviations, and explanations of terminology for information system security. The 334 pages of entries offer recommendations to improve the comprehensibility of written material that is generated in the Internet Standards Process (RFC 2026). The recommendations follow the principles that such writing should (a) use the same term or definition whenever the same concept is mentioned; (b) use terms in their plainest, dictionary sense; (c) use terms that are already well-established in open publications; and (d) avoid terms that either favor a particular vendor or favor a particular technology or mechanism over other, competing techniques that already exist or could be developed. This memo provides information for the Internet community. JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data. This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance. Combitech Ericsson Spotify AB Arm Ltd. This specification defines a framework for authentication and authorization in Internet of Things (IoT) environments called ACE- OAuth. The framework is based on a set of building blocks including OAuth 2.0 and the Constrained Application Protocol (CoAP), thus transforming a well-known and widely used authorization solution into a form suitable for IoT devices. Existing specifications are used where possible, but extensions are added and profiles are defined to better serve the IoT use cases. I-JSON (short for "Internet JSON") is a restricted profile of JSON designed to maximize interoperability and increase confidence that software can process it successfully with predictable results. The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack. This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format. The methods defined in RFC 7252 for the Constrained Application Protocol (CoAP) only allow access to a complete resource, not to parts of a resource. In case of resources with larger or complex data, or in situations where resource continuity is required, replacing or requesting the whole resource is undesirable. Several applications using CoAP need to access parts of the resources. This specification defines the new CoAP methods, FETCH, PATCH, and iPATCH, which are used to access and update parts of a resource. The Internet of Things (IoT) concept refers to the usage of standard Internet protocols to allow for human-to-thing and thing-to-thing communication. The security needs for IoT systems are well recognized, and many standardization steps to provide security have been taken -- for example, the specification of the Constrained Application Protocol (CoAP) secured with Datagram Transport Layer Security (DTLS). However, security challenges still exist, not only because there are some use cases that lack a suitable solution, but also because many IoT devices and systems have been designed and deployed with very limited security capabilities. In this document, we first discuss the various stages in the lifecycle of a thing. Next, we document the security threats to a thing and the challenges that one might face to protect against these threats. Lastly, we discuss the next steps needed to facilitate the deployment of secure IoT systems. This document can be used by implementers and authors of IoT specifications as a reference for details about security considerations while documenting their specific security challenges, threat models, and mitigations. This document is a product of the IRTF Thing-to-Thing Research Group (T2TRG). A URI Template is a compact sequence of characters for describing a range of Uniform Resource Identifiers through variable expansion. This specification defines the URI Template syntax and the process for expanding a URI Template into a URI reference, along with guidelines for the use of URI Templates on the Internet. [STANDARDS-TRACK] The Internet Protocol Suite is increasingly used on small devices with severe constraints on power, memory, and processing resources, creating constrained-node networks. This document provides a number of basic terms that have been useful in the standardization work for constrained-node networks. IANA IANA This document describes the Network File System (NFS) version 4 minor version 1, including features retained from the base protocol (NFS version 4 minor version 0, which is specified in RFC 7530) and protocol extensions made subsequently. The later minor version has no dependencies on NFS version 4 minor version 0, and is considered a separate protocol. This document obsoletes RFC 5661. It substantially revises the treatment of features relating to multi-server namespace, superseding the description of those features appearing in RFC 5661.

Acknowledgements , , , , and provided comments that shaped the direction of this document. pointed out that there were gaps in the media type specifications, and provided a shepherd review with further comments. provided an extensive review as responsible Area Director, and indeed is responsible for much improvement in the document.