wdiff draft-ietf-ace-oauth-authz-01.txt draft-ietf-ace-oauth-authz-02.txt

ACE Working Group L. Seitz
Internet-Draft SICS
Intended status: Standards Track G. Selander
Expires: August 28, December 12, 2016 Ericsson
E. Wahlstroem
S. Erdtman
Nexus Technology
S. Erdtman
Spotify AB
H. Tschofenig
ARM Ltd.
February 25,
June 10, 2016

Authentication and Authorization for the Internet of Things using OAuth 2.0
draft-ietf-ace-oauth-authz-01 Constrained Environments (ACE)
draft-ietf-ace-oauth-authz-02

Abstract

This memo specification defines how to use OAuth 2.0 as an authorization the ACE framework
with for authentication and
authorization in Internet of Things (IoT) deployments, deployments. The ACE
framework is based on a set of building blocks including OAuth 2.0
and CoAP, thus bringing making a well-known and widely used security authorization
solution to suitable for IoT devices. Where possible
vanilla OAuth 2.0 is used, Existing specifications are used
where possible, but where the limitations of IoT devices require it,
profiles and extensions are provided.

Status of This Memo

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provisions of BCP 78 and BCP 79.

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This Internet-Draft will expire on August 28, December 12, 2016.

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5
3.1. OAuth 2.0 . . . . . . . . . . . . . . . . . . . . . . . . 5 6
3.2. CoAP . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Object Security 8
4. Protocol Interactions . . . . . . . . . . . . . . . . . . . . 9
5. Framework . 8
4. Protocol Interactions . . . . . . . . . . . . . . . . . . . . 9
5. OAuth 2.0 Profiling . . . . . 13
6. The 'Token' Resource . . . . . . . . . . . . . . . . 12
5.1. Client Information . . . . 14
6.1. Client-to-AS Request . . . . . . . . . . . . . . . 12
5.2. CoAP Access-Token Option . . . 14
6.2. AS-to-Client Response . . . . . . . . . . . . . 15
5.3. Authorization Information Resource at the Resource Server 15
5.3.1. Authorization Information Request . . . . . 17
6.3. Error Response . . . . . 16
5.3.2. Authorization Information Response . . . . . . . . . 16
5.3.2.1. Success . . . . . . . 18
6.4. New Request and Response Parameters . . . . . . . . . . . 18
6.4.1. Grant Type . . . . . 16
5.3.2.2. Error Response . . . . . . . . . . . . . . . . 19
6.4.2. Token Type and Algorithms . 16
5.4. Authorization Information Format . . . . . . . . . . . . 17
5.5. . 19
6.4.3. Profile . . . . . . . . . . . . . . . . . . . . . . . 20
6.4.4. Confirmation . . . . . . . . . . . . . . . . . . . . 20
6.5. Mapping parameters to CBOR Data Formats . . . . . . . . . . . . . . . 22
7. The 'Introspect' Resource . . . . . 17
5.6. Token Expiration . . . . . . . . . . . . . 22
7.1. RS-to-AS Request . . . . . . . 17
6. Deployment Scenarios . . . . . . . . . . . . . 23
7.2. AS-to-RS Response . . . . . . . 18
6.1. Client and Resource Server are Offline . . . . . . . . . 19
6.2. Resource Server Offline . . . . 23
7.3. Error Response . . . . . . . . . . . . . 22
6.3. . . . . . . . . 24
7.4. Client Token . . . . . . . . . . . . . . . . . . . . . . 25
7.5. Mapping Introspection with an Offline Client parameters to CBOR . . . . . . . . 26
6.4. Always-On Connectivity
8. The Access Token . . . . . . . . . . . . . . . . . 30
6.5. Token-less Authorization . . . . . 27
8.1. The 'Authorization Information' Resource . . . . . . . . 27
8.2. Token Expiration . . . . 31
6.6. Securing Group Communication . . . . . . . . . . . . . . 34
7. . . 28
9. Security Considerations . . . . . . . . . . . . . . . . . . . 35
8. 28
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
8.1. CoAP Option Number 29
10.1. OAuth Introspection Response Parameter Registration . . 29
10.2. OAuth Parameter Registration . . . . . . . . . . . 35
9. Acknowledgments . . . 30
10.3. OAuth Access Token Types . . . . . . . . . . . . . . . . 30
10.4. Token Type Mappings . . . . 36
10. References . . . . . . . . . . . . . . 30
10.4.1. Registration Template . . . . . . . . . . . 36
10.1. Normative References . . . . 30
10.4.2. Initial Registry Contents . . . . . . . . . . . . . 31
10.5. JSON Web Token Claims . 36
10.2. Informative References . . . . . . . . . . . . . . . . 31
10.6. ACE Profile Registry . 38
Appendix A. Design Justification . . . . . . . . . . . . . . . . 40
Appendix B. Roles and Responsibilites -- a Checklist . 31
10.6.1. Registration Template . . 41
Appendix C. Optimizations . . . . . . . . . . . . . 31
10.7. OAuth Parameter Mappings Registry . . . . . . 44
Appendix D. CoAP and CBOR profiles for OAuth 2.0 . . . . . 32
10.7.1. Registration Template . . . 45
D.1. Profile for Token resource . . . . . . . . . . . . 32
10.7.2. Initial Registry Contents . . . 45
D.1.1. Token Request . . . . . . . . . . 32
10.8. Introspection Resource CBOR Mappings Registry . . . . . 34
10.8.1. Registration Template . . . . . 46
D.1.2. Token Response . . . . . . . . . . 35
10.8.2. Initial Registry Contents . . . . . . . . . 47

D.2. . . . . 35
10.9. CoAP Profile for OAuth Introspection Option Number Registration . . . . . . . . . . . 48
D.2.1. Introspection Request . 37
11. Acknowledgments . . . . . . . . . . . . . . . 48
D.2.2. Introspection Response . . . . . . . . 37
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
12.1. Normative References . . . . . . . . . . . . . . . . . 49 . 38
12.2. Informative References . . . . . . . . . . . . . . . . . 38
Appendix E. A. Design Justification . . . . . . . . . . . . . . . . 40
Appendix B. Roles and Responsibilites . . . . . . . . . . . . . 42
Appendix C. Deployment Examples . . . . . . . . . . . . . . . . 44
C.1. Local Token Validation . . . . . . . . . . . . . . . . . 44
C.2. Introspection Aided Token Validation . . . . . . . . . . 48
Appendix D. Document Updates . . . . . . . . . . . . . . . . . . 51
E.1.
D.1. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 52
D.2. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 51 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52 53

1. Introduction

Authorization is the process for granting approval to an entity to
access a resource [RFC4949]. Managing authorization information for
a large number of devices and users is often a complex task where
dedicated servers are used.

Managing authorization of users, services and their devices with the
help of dedicated authorization servers (AS) is a common task, found
in enterprise networks as well as on the Web. In its simplest form
the The authorization task itself can best
be described as granting access to a requesting client, for a
resource hosted on a device, the resource server (RS). This exchange
is mediated by one or multiple authorization servers. servers (AS). Managing
authorization for a large number of devices and users is a complex
task.

We envision that end consumers and enterprises will want to manage
access-control and authorization for their access to
resources on, or produced by, Internet of Things (IoT) devices in the
same style as they do today with data, services and this applications on
the Web or with their mobile devices. This desire will increase with
the number of exposed services and capabilities provided by
applications hosted on the IoT devices. The

While prior work on authorization solutions for the Web and for the
mobile environment also applies to the IoT environment many IoT
devices may be constrained are constrained, for example in
various ways including processing, terms of processing
capabilities, available memory, code-size, energy, etc.,
as defined etc. For web applications on
constrained nodes this specification makes use of CoAP [RFC7252].

A detailed treatment of constraints can be found in [RFC7228], and
the different IoT deployments present a continuous range of device
and network capabilities. Taking energy consumption as an example:

At one end there are energy-harvesting or battery powered devices
which have a tight power budget, on the other end there are devices connected to a continuous power supply which
are not constrained in terms of power, mains-
powered devices, and all levels in between.
Thus

Hence, IoT devices are may be very different in terms of available
processing and message exchange capabilities. capabilities and there is a need to
support many different authorization use cases [RFC7744].

This memo specification describes how to a framework for authentication and
authorization in constrained environments (ACE) built on re-use of
OAuth 2.0 [RFC6749] to extend [RFC6749], thereby extending authorization to Internet of
Things devices with different kinds of
constraints. At devices. This specification contains the time of writing, necessary building
blocks for adjusting OAuth 2.0 is already used with
certain types of to IoT devices and this document will provide
implementers additional guidance for using it environments.

More detailed, interoperable specifications can be found in profiles.
Implementations may claim conformance with a secure and
privacy-friendly way. Where possible specific profile,
whereby implementations utilizing the basic OAuth 2.0 mechanisms
are used; in some circumstances same profile interoperate while
implementations of different profiles are defined, for example not expected to
support smaller the over-the-wire message size be
interoperable. Some devices, such as mobile phones and smaller code size. tablets, may
implement multiple profiles and will therefore be able to interact
with a wider range of low end devices.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].

Certain security-related terms such as "authentication",
"authorization", "confidentiality", "(data) integrity", "message
authentication code", and "verify" are taken from [RFC4949].

Since we describe exchanges as RESTful protocol interactions HTTP
[RFC7231] offers useful terminology.

Terminology for entities in the architecture is defined in OAuth 2.0
[RFC6749] and [I-D.ietf-ace-actors], such as client (C), resource
server (RS), and authorization server (AS). OAuth 2.0 uses

Note that the term "endpoint" is used here following its OAuth
definition, which is to denote HTTP resources such as /token and /authorize
/introspect at the AS, but we will use AS and /authz-info at the term "resource" RS. The CoAP [RFC7252]
definition, which is "An entity participating in this memo to avoid
confusion with the CoAP [RFC7252] term "endpoint". protocol"
is not used in this memo.

Since this draft specification focuses on the problem of access control to
resources, we simplify the actors by assuming that the client
authorization server (CAS) functionality is not stand-alone but
subsumed by either the authorization server or the client (see
section 2.2 in [I-D.ietf-ace-actors]).

3. Overview

This specification describes a the ACE framework for authorization in
the Internet of Things consisting of a set of building blocks.

The basic block is the OAuth 2.0 [RFC6749] framework, which enjoys
widespread deployment. Many IoT devices can support OAuth 2.0
without any additional extensions, but for certain constrained
settings additional profiling is needed.

Another building block is the lightweight web transfer protocol CoAP
[RFC7252] for those communication environments where HTTP is not
appropriate. CoAP typically runs on top of UDP which further reduces
overhead and message exchanges. Transport layer security can While this specification defines
extensions for the use of OAuth over CoAP, we do envision further
underlying protocols to be
provided either by DTLS 1.2 [RFC6347] supported in the future, such as MQTT or TLS 1.2 [RFC5246].
QUIC.

A third building block is CBOR [RFC7049] for encodings where JSON
[RFC7159] is not sufficiently compact. CBOR is a binary encoding
designed for extremely small code size and fairly small message size.
OAuth 2.0 allows access tokens to use different encodings size, which may be used for
encoding of self contained tokens, and this
document defines such an alternative encoding. The COSE message
format [I-D.ietf-cose-msg] is also based on CBOR. for encoding CoAP POST
parameters and CoAP responses.

A fourth building block is the compact CBOR-based secure message
format COSE [I-D.ietf-cose-msg], which enables application layer security, which is used
where
security as an alternative or complement to transport layer security
(DTLS [RFC6347] or TLS [RFC5246]). COSE is insufficient. At the time of
writing the preferred approach for securing CoAP at the application
layer used to secure self
contained tokens such as proof-of-possession (PoP) tokens
[I-D.ietf-oauth-pop-architecture], which is via an extension to the use of COSE [I-D.ietf-cose-msg], OAuth
access tokens, and "client tokens" which adds object are defined in this
framework (see Section 7.4). The default access token format is
defined in CBOR web token (CWT) [I-D.ietf-ace-cbor-web-token].
Application layer security to CBOR-encoded data. More details about applying COSE to for CoAP using COSE can be found in provided with
OSCOAP [I-D.selander-ace-object-security].

With the building blocks listed above, solutions satisfying various
IoT device and network constraints are possible. A list of
constraints is described in detail in RFC 7228 [RFC7228] and a
description of how the building blocks mentioned above relate to the
various constraints can be found in Appendix A.

Luckily, not every IoT device suffers from all constraints. The
described ACE
framework nevertheless takes all these aspects into account and
allows several different deployment variants to co-exist rather than
mandating a one-size-fits-all solution. We believe this is important
to cover the wide range of possible interworking use cases and the
different requirements from a security point of view. Once IoT
deployments mature, popular deployment variants will be documented in
form of ACE profiles.

In the subsections below we provide further details about the
different building blocks.

3.1. OAuth 2.0

The OAuth 2.0 authorization framework enables a client to obtain
limited access to a resource with the permission of a resource owner.
Authorization related information information, or references to it, is passed between the
nodes using access tokens. These access tokens are issued to clients
by an authorization server with the approval of the resource owner.
The client uses the access token to access the protected resources
hosted by the resource server.

A number of OAuth 2.0 terms are used within this memo: specification:

The token and introspect Endpoints:

The AS hosts the /token endpoint that allows a client to request
access tokens. The client makes a POST request to the /token
endpoint on the AS and receives the access token in the response
(if the request was successful).

The token introspection endpoint, /introspect, is used by the RS
when requesting additional information regarding a received access
token. The RS makes a POST request to /introspect on the AS and
receives information about the access token contain in the
response. (See "Introspection" below.)

Access Tokens:

Access tokens are credentials used needed to access protected
resources. An access token is a data structure representing
authorization permissions issued by the AS to the client. Access
tokens are generated by the authorization server and consumed by
the resource server. The access token content is opaque to the
client.

Access tokens can have different formats, and various methods of
utilization (e.g., cryptographic properties) based on the security
requirements of the given deployment.

Proof of Possession Tokens:

An access token may be bound to a cryptographic key, which is then
used by an RS to authenticate requests from a client. Such tokens
are called proof-of-possession tokens (or PoP tokens)
[I-D.ietf-oauth-pop-architecture].

The proof-of-possession (PoP) security concept assumes that the AS
acts as a trusted third party that binds keys to access tokens.
These so called PoP keys are then used by the client to
demonstrate the possession of the secret to the RS when accessing
the resource. The RS, when receiving an access token, needs to
verify that the key used by the client matches the one included in
the access token. When this memo specification uses the term "access
token" it is assumed to be a PoP token unless specifically stated
otherwise.

The key bound to the access token (aka PoP key) may be based on
symmetric as well as on asymmetric cryptography. The appropriate
choice of security depends on the constraints of the IoT devices
as well as on the security requirements of the use case.

Symmetric PoP key: The AS generates a random symmetric PoP key,
encrypts it for the RS and includes it inside an access token.
The PoP key is also encrypted for the client and sent together
with the access token to the client. client.>

Asymmetric PoP key: An asymmetric key pair is generated on the
client and the public key is sent to the AS (if it does not
already have knowledge of the client's public key).
Information about the public key, which is the PoP key in this
case, is then included inside the access token and sent back to
the requesting client. The RS can identify the client's public
key from the information in the token, which allows the client
to use the corresponding private key for the proof of
possession.

The access token is protected against modifications using a MAC or
a digital signature of signature, which is added by the AS. The choice of PoP
key does not necessarily imply a specific credential type for the
integrity protection of the token. More information about PoP
tokens can be found in [I-D.ietf-oauth-pop-architecture].

Scopes and Permissions:

In OAuth 2.0, the client specifies the type of permissions it is
seeking to obtain (via the scope parameter) in the access request.
In turn, the AS may use the "scope" scope response parameter to inform the
client of the scope of the access token issued. As the client
could be a constrained device as well, this memo specification uses
CBOR encoded messages for CoAP, defined in Appendix D Section 5, to request
scopes and to be informed what scopes the access token was
actually authorized for by the AS.

The values of the scope parameter are expressed as a list of
space- delimited, case-sensitive strings, with a semantic that is
well-known to the AS and the RS. More details about the concept
of scopes is found under Section 3.3 in [RFC6749].

Claims:

The information

Information carried in the access token token, called claims, is in the
form of type-
value pairs is called claims. type-value pairs. An access token may may, for example example,
include a claim about identifying the AS that issued the token (the (via the
"iss" claim) and what audience the access token is intended for (the
(via the "aud" claim). The audience of an access token can be a
specific resource or one or many resource servers. The resource
owner policies influence the what claims are put into the access token
by the authorization server.

While the structure and encoding of the access token varies
throughout deployments, a standardized format has been defined
with the JSON Web Token (JWT) [RFC7519] where claims are encoded
as a JSON object. In [I-D.wahlstroem-ace-cbor-web-token] [I-D.ietf-ace-cbor-web-token] an equivalent
format using CBOR encoding (CWT) has been defined.

Introspection:

Introspection is a method for a resource server to query the
authorization server for the active state and content of a
received access token. This is particularly useful in those cases
where the authorization decisions are very dynamic and/or where
the received access token itself is a reference rather than a
self-contained token. More information about introspection in
OAuth 2.0 can be found in [I-D.ietf-oauth-introspection]. [RFC7662].

3.2. CoAP

CoAP is an application layer protocol similar to HTTP, but
specifically designed for constrained environments. CoAP typically
uses datagram-oriented transport, such as UDP, where reordering and
loss of packets can occur. A security solution need to take the
latter aspects into account.

While HTTP uses headers and query-strings to convey additional
information about a request, CoAP encodes such information in so-
called 'options'.

CoAP supports application-layer fragmentation of the CoAP payloads
through blockwise transfers [I-D.ietf-core-block]. However, this
method block-
wise transfer does not allow increase the fragmentation size limits of large CoAP options,
therefore data encoded in options has to be kept small.

3.3. Object Security

Transport layer security is not always sufficient and application
layer security has to for CoAP can be provided. COSE [I-D.ietf-cose-msg] provided by DTLS 1.2
[RFC6347] or TLS 1.2 [RFC5246]. CoAP defines a message format for cryptographic protection number of data using CBOR
encoding. There are two main approaches for application proxy
operations which requires transport layer
security:

Object Security of CoAP (OSCOAP)

OSCOAP [I-D.selander-ace-object-security] is a method security to be terminated
at the proxy. One approach for protecting CoAP request/response message exchanges, including CoAP
payloads, communication end-to-
end through proxies, and also to support security for CoAP header fields as well over
different transport in a uniform way, is to provide security on
application layer using an object-based security mechanism such as CoAP options.
CBOR Encoded Message Syntax [I-D.ietf-cose-msg].

One application of COSE is OSCOAP [I-D.selander-ace-object-security],
which provides end-to-end confidentiality, integrity and replay
protection, and a secure binding between CoAP request and response
messages.

A CoAP message protected with OSCOAP contains the CoAP option
"Object-Security" which signals that the CoAP message carries a
COSE message ([I-D.ietf-cose-msg]). OSCOAP defines a profile of
COSE which includes replay protection.

Object Security of Content (OSCON)

For the case of wrapping of application layer payload data
("content") only, such as resource representations or claims of
access tokens, the same COSE profile can be applied to obtain end-
to-end confidentiality, integrity and replay protection.
[I-D.selander-ace-object-security] defines this functionality as
Object Security of Content (OSCON). In this case, the message is not bound to OSCOAP, the underlying
application layer protocol and can therefore be used with HTTP,
CoAP, Bluetooth Smart, etc. While OSCOAP integrity protects
specific CoAP message meta-data like request/response code, and
binds a response to a specific request, OSCON protects only
payload/content, therefore those security features are lost. The
advantages messages are that an OSCON message can be passed across
different protocols, from request to response, wrapped in COSE objects
and used to secure
group communications. sent using CoAP.

4. Protocol Interactions

This

The ACE framework is based on the same OAuth 2.0 protocol interactions as OAuth
2.0:
using the /token and /introspect endpoints. A client obtains an
access token from an AS using the /token endpoint and subsequently
presents the access token to an a RS to gain access to a protected
resource. The RS, after receiving an access token, may present it to
the AS via the /introspect endpoint to get information about the
access token. In other deployments the RS may process the access
token locally without the need to contact an AS. These interactions
are shown in Figure 1. An overview of various OAuth concepts is
provided in Section 3.1.

The consent of the resource owner, for giving a client access to a
protected resource, can be pre-configured authorization policies or
dynamically at the time when the request is sent. The resource owner
and the requesting party (= (i.e. client owner) are not shown in
Figure 1.

For

This framework supports a wide variety of communication security
mechanisms between the description in this document we ACE entities, such as client, AS, and RS. We
assume that the client has been registered (also called enrolled or
onboarded) to an AS. Registration means AS using a mechanism defined outside the scope of
this document. In practice, various techniques for onboarding have
been used, such as factory-based provisioning or the use of
commissioning tools. Regardless of the onboarding technique, this
registration procedure implies that the two client and the AS share
credentials, configuration parameters and that some form of
authorization has taken place. configuration parameters. These credentials are
used to mutually authenticate each other and to protect
the token request by messages
exchanged between the client and the transport of access tokens
and client information from AS to the client. AS.

It is also assumed that the RS has been registered with the AS,
potentially in a similar way as the client has been registered with
the AS. Established keying material between the AS and the RS allows
the AS to apply cryptographic protection to the access token to
ensure that
the its content cannot be modified, and if needed, that the
content is confidentiality protected.

The keying material necessary for establishing communication security
between C and RS is dynamically established as part of the protocol
described in this document.

At the start of the protocol there is an optional discovery step
where the client discovers the resource server and the resources this
server hosts. In this step the client might also determine what
permissions are needed to access the protected resource. The exact
procedure depends
detailed procedures for this discovery process may be defined in an
ACE profile and depend on the protocols being used and the specific
deployment environment.

In Bluetooth Smart, Low Energy, for example, advertisements are broadcasted
by a peripheral, including information about the supported primary services.
In CoAP, as a second example, a client can makes a request to
"/.well-known/core" to obtain information about available resources,
which are returned in a standardized format as described in
[RFC6690].

+--------+ +---------------+
| |---(A)-- Token Request ------------->| ------->| |
| | | Authorization |
| |<--(B)-- Access Token ---------------| ---------| Server |
| | + Client Information | |
| | +---------------+
| | ^ |
| | Introspection Request & Response (D)| |(E) |
| Client | | |
| | Response + Client Token | |(E)
| | | v
| | +--------------+
| |---(C)-- Token + Request ----------->| ----->| |
| | | Resource |
| |<--(F)-- Protected Resource ---------| ---| Server |
| | | |
+--------+ +--------------+

Figure 1: Overview of the basic protocol flow Basic Protocol Flow.

Requesting an Access Token (A):

The client makes an access token request to the /token endpoint at
the AS. This memo framework assumes the use of PoP tokens (see
Section 3.1 for a short description) wherein the AS binds a key to
an access token. The client may include permissions it seeks to
obtain, and information about the type of credentials it wants to use (i.e., symmetric
(e.g., symmetric/asymmetric cryptography or
asymmetric cryptography). a reference to a
specific credential).

Access Token Response (B):

If the AS successfully processes the request from the client, it
returns an access token. It also includes returns various parameters,
which we call
referred as "Client Information". In addition to the response
parameters defined by OAuth 2.0 and the PoP token extension, we
consider new kinds of
further response parameters in Section 5, including parameters, such as information on which security protocol profile
the client should use with the resource server(s) that it has just been authorized to access.
Communication security between client and RS may be based on pre-
provisioned keys/security contexts or dynamically established.
The RS authenticates the client via the PoP token; and the client
authenticates the RS via the client server(s). More
information as described about these parameters can be found in in Section 5.1. 6.4.

Resource Request (C):

The client interacts with the RS to request access to the
protected resource and provides the access token. The protocol to
use between the client and the RS is not restricted to CoAP; CoAP.
HTTP, HTTP/2, QUIC, MQTT, Bluetooth Smart Low Energy, etc., are also possible
viable candidates.

Depending on the device limitations and the selected protocol this
exchange may be split up into two phases: parts:

(1) the client sends the access token to a newly defined
authorization endpoint at containing, or
referencing, the RS (see Section 5.3) , which
conveys authorization information to the RS RS, that may
be used by
the client for subsequent resource requests, requests by the client, and
(2) the client makes the resource access request, using the
communication security protocol and other client information
obtained from the AS.

The Client and the RS mutually authenticate using the security
protocol specified in the profile (see step B) and the keys
obtained in the access token or the client information or the
client token. The RS verifies that the token is integrity
protected by the AS and compares the claims contained in the
access token with the resource request. If the RS is online,
validation can be handed over to the AS using token introspection
(see messages D and E) over HTTP or CoAP, in which case the
different parts of step C may be interleaved with introspection.

Token Introspection Request (D):

A resource server may be configured to use token introspection to
interact with introspect the AS access token
by including it in a request to obtain the most recent claims, such as
scope, audience, validity etc. associated with a specific access
token. /introspect endpoint at that
AS. Token introspection over CoAP is defined in
[I-D.wahlstroem-ace-oauth-introspection] Section 7 and for
HTTP in
[I-D.ietf-oauth-introspection]. [RFC7662].

Note that token introspection is an optional step and can be
omitted if the token is self-contained and the resource server is
prepared to perform the token validation on its own.

Token Introspection Response (E):

The AS validates the token and returns the claims most recent parameters,
such as scope, audience, validity etc. associated with it back to
the RS. The RS then uses the received claims parameters to process the
request to either accept or to deny it. The AS can additionally
return information that the RS needs to pass on to the client in
the form of a client token. The latter is used to establish keys
for mutual authentication between client and RS, when the client
has no direct connectivity to the AS.

Protected Resource (F):

If the request from the client is authorized, the RS fulfills the
request and returns a response with the appropriate response code.
The RS uses the dynamically established keys to protect the
response, according to used communication security protocol.

5. OAuth 2.0 Profiling

This section describes profiles Framework

The following sections detail the profiling and extensions of OAuth
2.0 adjusting it to for constrained environments for use cases where this which constitutes the ACE framework.

Credential Provisioning

For IoT we cannot generally assume that the client and RS are part
of a common key infrastructure, so the AS provisions credentials
or associated information to allow mutual authentication. These
credentials need to be provided to the parties before or during
the authentication protocol is necessary.
Profiling executed, and may be re-used for JSON Web Tokens (JWT)
subsequent token requests.

Proof-of-Possession

The ACE framework by default implements proof-of-possession for
access tokens, i.e. that the authenticated token holder is bound
to the token. The binding is provided in
[I-D.wahlstroem-ace-cbor-web-token].

5.1. Client Information

OAuth 2.0 using bearer tokens, by the "cnf" claim
indicating what key is used for mutual authentication. If clients
need to update a token, e.g. to get additional rights, they can
request that the AS binds the new access token to the same
credential as described the previous token.

ACE Profile Negotiation

The client or RS may be limited in [RFC6749] the encodings or protocols it
supports. To support a variety of different deployment settings,
specific interactions between client and RS are defined in
[RFC6750], requires TLS for all communication interactions an ACE
profile. The ACE framework supports the negotiation of different
ACE profiles between
client, authorization server, client and resource server. This is possible AS using the "profile" parameter
in the scope where token request and token response.

OAuth 2.0 was originally developed: web requires the use of TLS both to protect the communication
between AS and mobile
applications. In these environments resources like computational
power client when requesting an access token and bandwidth are not scarce between AS
and operating systems as well as
browser platforms are pre-provisioned with trust anchors RS for introspection. In constrained settings TLS is not always
feasible, or desirable. Nevertheless it is REQUIRED that enable
clients to authenticate servers based on the Web PKI. In a more
heterogeneous IoT environment a wider range of use cases needs to be
supported. Therefore, this document suggests extensions to OAuth 2.0 data
exchanged with the AS is encrypted and integrity protected. It is
furthermore REQUIRED that enables the AS and the endpoint communicating with
it (client or RS) perform mutual authentication.

Profiles are expected to inform specify the client on details of how to communicate
securely with a RS this is done,
depending e.g. on the communication protocol and that allows the credentials used
by the client to indicate
communication security preferences to or the AS. RS.

In the OAuth memo defining 2.0 the key distribution for proof-of-
possession (PoP) tokens [I-D.ietf-oauth-pop-key-distribution], communication with the Token and the Introspection
resources at the
authors suggest AS is assumed to be via HTTP and may use Uri-query parameters in order
parameters. This framework RECOMMENDS to submit the
parameters of the client's token request. To avoid large headers if
the client uses use CoAP to communicate with instead and
RECOMMENDS the AS, this memo specifies use of the following alternative for submitting client request parameters to
the AS: instead of Uri-query
parameters: The client sender (client or RS) encodes the parameters of it's its
request as a CBOR map and submits that map as the payload of the client POST
request. The Content-format MUST be application/cbor "application/cbor" in that case.

The OAuth memo further specifies that the 2.0 AS SHALL use uses a JSON structure in the payload of the response its
responses both to encode the response
parameters. These parameters include the access token, destined for
the RS and additional information for the client, such as e.g. the
PoP key. We call this information "client information". If the client is using CoAP to communicate with the AS and RS. This framework RECOMMENDS the AS SHOULD use
CBOR instead
of JSON for encoding it's response. CBOR [RFC7049] instead. The client requesting device can explicitly
request this encoding by using setting the CoAP Accept option.

If the channel between client and AS is not secure, the whole
messages from client to AS and vice-versa MUST be wrapped in JWEs
[RFC7516] or COSE_Encrypted structures [I-D.ietf-cose-msg].

The client may be a constrained device and could therefore be limited option in the communication security protocols it supports. It can
therefore signal
request to "application/cbor".

6. The 'Token' Resource

In plain OAuth 2.0 the AS which protocols it can support provides the /token resource for
securing their mutual communication. submitting
access token requests. This is done by using framework extends the "csp"
parameter defined below in functionality of
the Token Request message sent to /token resource, giving the AS.

Note that The OAuth key distribution specification
[I-D.ietf-oauth-pop-key-distribution] describes in section 6 how AS the possibility to help client can request specific types of keys (symmetric vs. asymmetric) and proof-of-possession algorithms in
RS to establish shared keys or to exchange their public keys.

Communication between the PoP token request.

The client and the RS might not have any prior knowledge about each
other, therefore token resource at the AS needs to help them to establish a security
context or at least a key. The
MUST be integrity protected and encrypted. Furthermore AS does this by indicating
communication security protocol ("csp") and additional key parameters
in the client information.

The "csp" parameter specifies
MUST perform mutual authentication. Profiles of this framework are
expected to specify how client authentication and RS communication security is
going to be secured based on returned keys. Currently defined values
are "TLS", "DTLS", "ObjectSecurity" with
implemented.

The figures of this section uses CBOR diagnostic notation without the encodings specified in
Figure 2. Depending on
integer abbreviations for the value different additional parameters
become mandatory.

/-----------+--------------+-----------------------\
| Value | Major Type | Key |
|-----------+--------------+-----------------------|
| 0 | 0 | TLS |
| 1 | 0 | DTLS |
| 2 | 0 | ObjectSecurity |
\-----------+--------------+-----------------------/

Figure 2: Table of 'csp' parameter value encodings or their values for Client
Information.

CoAP specifies three security modes of DTLS: PreSharedKey,
RawPublicKey and Certificate. The same modes may be used with TLS.
The client is to infer better
readability.

6.1. Client-to-AS Request

When requesting an access token from the type of key provided, which (D)TLS
mode AS, the RS supports as follows.

If PreSharedKey mode is used, client MAY include
the AS MUST provide following parameters in the client with request in addition to the
pre-shared key ones
required or optional according to be used with the RS. OAuth 2.0 specification
[RFC6749]:

token_type
OPTIONAL. See Section 6.4 for more details.

alg
OPTIONAL. See Section 6.4 for more details.

profile
OPTIONAL. This key MUST be indicates the same as profile that the PoP key (i.e. a symmetric key as in section 4 of
[I-D.ietf-oauth-pop-key-distribution]).

The client MUST would like
to use with the PoP key as DTLS pre-shared key. The client
MUST furthermore use RS. See Section 6.4 for more details on the "kid" parameter provided as part
formatting of this parameter. If the JWK/
COSE_Key as the psk_identity in RS cannot support the DTLS handshake [RFC4279].

If RawPublicKey mode is used,
requested profile, the AS MUST provide the client reply with the
RS's raw an error message.

cnf
OPTIONAL. This field contains information about a public key using the "rpk" parameter defined in
client would like to bind to the access token. If the
following. This parameter MUST contain a JWK or a COSE_Key. The client MUST
requests an asymmetric proof-of-possession algorithm, but does not
provide a raw public key to the AS, and key, the AS MUST use
this key as PoP key respond with an error message.
See Section 6.4 for more details on the formatting of the 'cnf'
parameter.

These new parameters are optional in the token. The token MUST thus use asymmetric
keys for case where the proof-of-possession.

In order to get AS has prior
knowledge of the capabilities of the client, otherwise these
parameters are required. This prior knowledge may, for example, be
set by the use of a dynamic client registration protocol exchange
[RFC7591].

The following examples illustrate different types of requests for
proof-of-possession tokens.

Figure 2 shows a RS configured request for a token with a symmetric proof-of-
possession key.

Header: POST (Code=0.02)
Uri-Host: "server.example.com"
Uri-Path: "token"
Content-Type: "application/cbor"
Payload:
{
"grant_type" : "client_credentials",
"aud" : "tempSensor4711",
"client_id" : "myclient",
"client_secret" : b64'FWRUVGZUZmZFRkWSRlVGhA',
"token_type" : "pop",
"alg" : "HS256",
"profile" : "coap_dtls"
}

Figure 2: Example request for an access token bound to use this
mode together a symmetric
key.

Figure 3 shows a request for a token with PoP tokens MUST require client authentication in
the DTLS handshake. The client MUST use the raw public an asymmetric proof-of-
possession key.

Header: POST (Code=0.02)
Uri-Host: "server.example.com"
Uri-Path: "token"
Content-Type: "application/cbor"
Payload:
{
"grant_type" : "token",
"aud" : "lockOfDoor0815",
"client_id" : "myclient",
"token_type" : "pop",
"alg" : "ES256",
"profile" : "coap_oscoap"
"cnf" : {
"COSE_Key" : {
"kty" : "EC",
"kid" : h'11',
"crv" : "P-256",
"x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
"y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
}
}
}

Figure 3: Example request for an access token bound to an asymmetric
key.

Figure 4 shows a request for a token where a previously communicated
proof-of-possession key is only referenced.

Header: POST (Code=0.02)
Uri-Host: "server.example.com"
Uri-Path: "token"
Content-Type: "application/cbor"
Payload:
{
"grant_type" : "client_credentials",
"aud" : "valve424",
"scope" : "read",
"client_id" : "myclient",
"token_type" : "pop",
"alg" : "ES256",
"profile" : "coap_oscoap"
"cnf" : {
"kid" : b64'6kg0dXJM13U'
}
}

Figure 4: Example request for an access token bound to a key
reference.

6.2. AS-to-Client Response

If the access token request has been successfully verified by the AS
and the client is authorized to obtain a PoP token for the indicated
audience and scopes (if any), the AS issues an access token. If
client authentication in DTLS.

TLS or DTLS with certificates MAY make use of pre-established trust
anchors failed or MAY be configured more tightly with additional client
information parameters, such is invalid, the authorization server
returns an error response as x5c, x5t, or x5t#S256. An overview
of these described in Section 6.3.

The following parameters is given below.

For when communication security is based on certificates this
attribute can may also be used part of a successful response in
addition to define those defined in section 5.1 of [RFC6749]:

profile
REQUIRED. This indicates the server certificate or CA
certificate. Semantics profile that the client MUST use
towards the RS. See Section 6.4 for the formatting of this attribute is defined by [RFC7517] or
COSE_Key [I-D.ietf-cose-msg].

For when communication security is based on certificates
parameter.

cnf
REQUIRED. This field contains information about the proof-of
possession key for this access token. See Section 6.4 for the
formatting of this
attribute parameter.

Note that the access token can be used to define also contains a 'cnf' claim, however,
these two values are consumed by different parties. The access token
is created by the specific server certificate AS and processed by the RS (and opaque to
expect or the CA certificate. Semantics for this attribute
client) whereas the Client Information is
defined created by JWK/COSE_Key.

To use object security (such as OSCOAP the AS and OSCON) requires security
context
processed by the client; it is never forwarded to be established, which can be provisioned with PoP the resource
server.

The following examples illustrate different types of responses for
proof-of-possession tokens.

Figure 5 shows a response containing a token and client information, or derived from that information. Object
security specifications designed to be used a 'cnf' parameter
with this protocol MUST
specify a symmetric proof-of-possession key.

Header: Created (Code=2.01)
Content-Type: "application/cbor"
Payload:
{
"access_token" : b64'SlAV32hkKG ...
(remainder of CWT omitted for brevity;
CWT contains COSE_Key in the parameters that an 'cnf' claim)',
"token_type" : "pop",
"alg" : "HS256",
"expires_in" : "3600",
"profile" : "coap_dtls"
"cnf" : {
"COSE_Key" : {
"kty" : "Symmetric",
"kid" : b64'39Gqlw',
"k" : b64'hJtXhkV8FJG+Onbc6mxCcQh'
}
}
}

Figure 5: Example AS has response with an access token bound to provide a
symmetric key.

6.3. Error Response

The error responses for CoAP-based interactions with the AS are
equivalent to the client ones for HTTP-based interactions as defined in
order to set up
section 5.2 of [RFC6749], with the necessary security context. following differences: The RS may support different ways of receiving
Content-Type MUST be set to "application/cbor", the payload MUST be
encoded in a CBOR map and the CoAP response code 4.00 Bad Request
MUST be used unless specified otherwise.

6.4. New Request and Response Parameters

This section defines parameters that can be used in access token from
the client (see Section 5.3
requests and Appendix C). responses, as well as abbreviations for more compact
encoding of existing parameters and common values.

6.4.1. Grant Type

The AS abbreviations in Figure 6 MAY signal the
required method for access token transfer be used in CBOR encodings instead
of the client information
by using the "tktr" (token transport) parameter using the string values defined in table Figure 3. If no "tktn" parameter is present, the
client MUST use the default Authorization Information resource as
specified in Section 5.3.

/-----------+--------------+-------------------------\ [RFC6749].

/--------------------+----------+--------------\
| grant_type | Value CBOR Key | Major Type | Key
|--------------------+----------+--------------|
|
|-----------+--------------+-------------------------| password | 0 | 0 (uint) | POST to /authz-info
| authorization_code | 1 | 0 | RFC 4680
| client_credentials | 2 | 0 | CoAP option "Ref-Token"
|
\-----------+--------------+-------------------------/ refresh_token | 3 | 0 |
\--------------------+----------+--------------/

Figure 3: Table of 'tktn' 6: CBOR abbreviations for common grant types

6.4.2. Token Type and Algorithms

To allow clients to indicate support for specific token types and
respective algorithms they need to interact with the AS. They can
either provide this information out-of-band or via the 'token_type'
and 'alg' parameter in the client request.

The value in the 'alg' parameter together with value encodings for Client
Information.

Table Figure 4 summarizes from the additional parameters defined here
'token_type' parameter allow the client to indicate the supported
algorithms for
use a given token type. The token type refers to the
specification used by the client or to interact with the AS in resource server
to demonstrate possession of the PoP key. The 'alg' parameter provides
further information about the algorithm, such as whether a symmetric
or an asymmetric crypto-system is used. Hence, a client supporting a
specific token request protocol.

/-----------+--------------+----------------------------------\
| Parameter | Used type also knows how to populate the values to the
'alg' parameter.

This document registers the new value "pop" for the OAuth Access
Token Types registry, specifying a Proof-of-Possession token. How
the proof-of-possession is performed is specified by | Description |
|-----------+--------------+----------------------------------|
| csp | the 'alg'
parameter. Profiles of this framework are responsible for defining
values for the 'alg' parameter together with the corresponding proof-
of-possession mechanisms.

The values in the 'alg' parameter are case-sensitive. If the client or AS | Communication
supports more than one algorithm then each individual value MUST be
separated by a space.

6.4.3. Profile

The "profile" parameter identifies the communication protocol and the
communication security protocol between the client and the RS.

An initial set of profile identifiers and their CBOR encodings are
specified in Figure 7. Profiles using other combinations of
protocols are expected to define their own profile identifiers.

/--------------------+----------+--------------\
| Profile identifier | rpk | AS | RS's raw public key |
| x5c | AS CBOR Key | RS's X.509 certificate chain Major Type |
|--------------------+----------+--------------|
| x5t http_tls | AS 0 | RS's SHA-1 cert thumb print 0 (uint) |
| x5t#S256 coap_dtls | AS 1 | RS's SHA-256 cert thumb print 0 |
| tktn coap_oscoap | AS 2 | Mode of token transfer C -> RS 0 |
\-----------+--------------+----------------------------------/
\--------------------+----------+--------------/

Figure 4: Table of 7: Profile identifiers and their CBOR mappings

Profiles MAY define additional parameters defined for both the PoP
protocol.

5.2. CoAP Access-Token Option

OAuth 2.0 access tokens are usually transferred as authorization
header. CoAP has no authorization header equivalence. This document
therefor register token request
and the option Access-Token. The Access-Token option
is an alternative for transferring client information in the access token when it is
smaller then 255 bytes. If token is larger the 255 bytes lager
authorization information resources MUST at response in order to
support negotioation or signalling of profile specific parameters.

6.4.4. Confirmation

The "cnf" parameter identifies or provides the RS be user when CoAP.

5.3. Authorization Information Resource at key used for proof-of-
possession. This framework extends the Resource Server

A consequence definition of allowing 'cnf' from
[RFC7800] by defining CBOR/COSE encodings and the use of CoAP as web transfer protocol is
that we cannot rely on HTTP specific mechanisms, such as transferring
information elements 'cnf' for
transporting keys in HTTP headers since those are not necessarily
gracefully mapped to CoAP. In case the access token is larger than
255 bytes it should not be sent as a CoAP option.

For conveying authorization information to client information.

A CBOR encoded payload MAY contain the RS a new resource is
introduced to which 'cnf' parameter with the PoP tokens can be sent to convey
authorization information before
following contents:

COSE_Key In this case the first resource request is made 'cnf' parameter contains the proof-of-
possession key to be used by the client. This specification calls this resource "/authz-info";
the URI may, however, vary An example is shown in deployments.

The RS needs to store
Figure 8.

"cnf" : {
"COSE_Key" : {
"kty" : "EC",
"kid" : h'11',
"crv" : "P-256",
"x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
"y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
}
}

Figure 8: Confirmation parameter containing a public key

COSE_Encrypted In this case the PoP token 'cnf' parameter contains an
encrypted symmetriic key destined for when later authorizing
requests from the client. The RS client is not mandated
assumed to be able to
manage multiple client at once. how decrypt the RS manages clients cihpertext of this parameter.
The parameter is out encoded as COSE_Encrypted object wrapping a
COSE_Key object. Figure 9 shows an example of
scope for this specification.

5.3.1. Authorization Information Request type of
encoding.

"cnf" : {
"COSE_Encrypted" : {
993(
[ h'a1010a' # protected header : {"alg" : "AES-CCM-16-64-128"}
"iv" : b64'ifUvZaHFgJM7UmGnjA', # unprotected header
b64'WXThuZo6TMCaZZqi6ef/8WHTjOdGk8kNzaIhIQ' # ciphertext
]
)
}
}

Figure 9: Confirmation paramter containing an encrypted symmetric key

The client makes ciphertext here could e.g. contain a POST request to the authorization information
resource by sending its PoP token symmetric key as request data.

Client MUST send in
Figure 10.

{
"kty" : "Symmetric",
"kid" : b64'39Gqlw',
"k" : b64'hJtXhkV8FJG+Onbc6mxCcQh'
}

Figure 10: Example plaintext of an encrypted cnf parameter

Key Identifier In this case the Content-Format option indicate token format

5.3.2. Authorization Information Response

The RS MUST resonde to 'cnf' parameter references a requests key
that is assumed to be previously known by the authorization information
resource. The response MUST match CoAP response codes according to
success or error response section

5.3.2.1. Success Response

Successful recipient. This
allows clients that perform repeated requests MUST be answered for an access token
for the same audience but e.g. with 2.01 Created different scopes to indicate
that a "session" for omit key
transport in the PoP Token has been created. No location
path is required access token, token request and token response.
Figure 11 shows such an example.

"cnf" : {
"kid" : b64'39Gqlw'
}

Figure 11: A Confirmation parameter with just a key identifier

6.5. Mapping parameters to be returned.

Resource
Client Server CBOR

All OAuth parameters in access token requests and responses are
mapped to CBOR types as follows and are given an integer key value to
save space.

/-------------------+----------+-----------------\
| Parameter name | CBOR Key | Major Type |
A: +-------->| Header: POST (Code=0.02)
|-------------------+----------+-----------------|
| POST client_id | Uri-Path: "/authz-info" 1 | 3 (text string) | Content-Format: "application/cwt"
| client_secret | Payload: <PoP Token> 2 | 2 (byte string) |
B: |<--------+ Header: 2.01 Created
| 2.01 response_type | 3 | 3 |
| redirect_uri | 4 | 3 |
| scope | 5 | 3 |
| state | 6 | 3 |
|

Figure 5: Authorization Information Resource Success Response

5.3.2.2. Error Response

The resource server MUST user appropriate CoAP response code to
convey the error to the Client. For request that are not valid, e.g.
unknown Content-Format, 4.00 Bad Request MUST be returned. If token
is not valid, e.g. wrong audience, the RS MUST return 4.01
Unauthorized.

Resource
Client Server | 7 | 2 |
|
A: +-------->| Header: POST (Code=0.02) error_description | POST 8 | Uri-Path: "/authz-info" 3 |
| Content-Format: "application/cwt" error_uri | 9 | Payload: <PoP Token> 3 |
|
B: |<--------+ Header: 4.01 Unauthorized grant_type | 2.01 10 | 0 (unit) |
| access_token | 11 | 3 |
| token_type | 12 | 0 |
| expires_in | 13 | 0 |
| username | 14 | 3 |
| password | 15 | 3 |
| refresh_token | 16 | 3 |
| alg | 17 | 3 |
| cnf | 18 | 5 (map) |
| aud | 19 | 3 |
| profile | 20 | 0 |
\---------------+--------------+-----------------/

Figure 6: Authorization Information Resource Error Response

5.4. Authorization Information Format

We introduce a new claim for describing access rights with a specific
format, the "aif" claim. In this memo we propose to use the compact
format provided by AIF [I-D.bormann-core-ace-aif]. Access rights may
be specified as a list of URIs of resources together with allowed
actions (GET, POST, PUT, PATCH, or DELETE). Other formats may be
mandated by specific applications or requirements (e.g. specifying
local conditions on access).

5.5. 12: CBOR Data Formats

The /token resource (called "endpoint" in OAuth 2.0), defined mappings used in
Section 3.2 of [RFC6749], token requests

7. The 'Introspect' Resource

Token introspection [RFC7662] is used by the client to obtain an access
token. Requests sent to the /token resource use the HTTP POST method RS and potentially the payload includes a
client to query component, which is formatted as
application/x-www-form-urlencoded. CoAP payloads cannot be formatted
in the same way which requires the /token resource on the AS to be
profiled. Appendix D defines a CBOR-based format for sending
parameters to the /token resource.

5.6. Token Expiration

Depending on the capabilities of the RS, there are various ways in
which it can verify the validity of metadata about a received access token. We list
the possibilities here including what functionality they require of
the RS.

o The given token is a CWT/JWT and includes a 'exp' claim and possibly the
'nbf' claim. The RS verifies these by comparing them e.g. validity
or scope. Analogous to values
from its internal clock as the protocol defined in [RFC7519]. In RFC 7662 [RFC7662]
for HTTP and JSON, this case section defines adaptations to more
constrained environments using CoAP and CBOR.

Communication between the RS must have a real time chip (RTC) or some other way of reliably
measuring time.

o The RS verifies the validity of and the token by performing an introspection request as specified in Appendix D.2. This requires
the RS to have a reliable network connection to resource at the AS and to
MUST be
able to handle two secure sessions in parallel (C to RS integrity protected and encrypted. Furthermore AS to
RS).

o The RS and RS
MUST perform mutual authentication. Finally the AS both store a sequence number linked SHOULD to their
common security association. The AS increments this number for
each access token it issues and includes it in the access token,
which is a CWT/JWT. The RS keeps track of the most recently
received sequence number, and only accepts tokens as valid, verify
that
are in a certain range around this number. This method does only
require the RS to keep track of has the sequence number. The method
does not provide timely expiration, but it makes sure that older
tokens cease right to be valid after a specified number of newer ones
got issued. For a constrained RS with no network connectivity and
no means of reliably measuring time, this is access introspection information about
the best that can be
achieved.

6. Deployment Scenarios

There is a large variety provided token. Profiles of IoT deployments, as is indicated in
Appendix A, and this section highlights common variants. This
section is not normative but illustrates how the framework can be
applied.

For each of the deployment variants there are a number of possible
security setups between clients, resource servers and authorization
servers. The main focus in the following subsections is on how
authorization of a client request for a resource hosted by a RS is
performed. This requires us expected to also consider
specify how these requests and
responses between the clients authentication and the resource servers are secured.

The communication security protocols between other pairs is implemented.

The figures of nodes in the
architecture, namely client-to-AS and RS-to-AS, are not detailed in
these examples. Different security protocols may be used on
transport or application layer.

Note: We use the this section uses CBOR diagnostic notation for examples of requests
and responses.

6.1. Client and Resource Server are Offline

In this scenario we consider the case where both without the resource server
and
integer abbreviations for the client are offline, i.e., they are not connected parameters or their values for better
readability.

7.1. RS-to-AS Request

The RS sends a CoAP POST request to the AS introspection resource at the time of the resource request. This access procedure involves
steps A, B, C, and F of Figure 1, but assumes that step A and B have
been carried out during
AS, with payload sent as "application/cbor" data. The payload is a phase when the client had connectivity to
AS.

Since the resource server must be able to verify
CBOR map with a 'token' parameter containing the access token
locally, self-contained access tokens must be used.

This example shows along
with optional parameters representing additional context that is
known by the interactions between a client, RS to aid the
authorization server AS in its response.

The same parameters are required and a temperature sensor acting optional as a resource
server. Message exchanges A and B are shown in section 2.1 of
RFC 7662 [RFC7662].

For example, Figure 7.

A: The client first generates 13 shows a public-private key pair used for
communication security with the RS.

The client sends RS calling the POST request to /token token introspection
resource at AS. The request
contains the public key of the client and the Audience parameter
set to "tempSensorInLivingRoom", a value that the temperature
sensor identifies itself with. The AS evaluates the request and
authorizes the client to access the resource.

B: query about an OAuth 2.0 proof-of-possession
token.

Header: POST (Code=0.02)
Uri-Host: "server.example.com"
Uri-Path: "introspect"
Content-Type: "application/cbor"
Payload:
{
"token" : b64'7gj0dXJQ43U',
"token_type_hint" : "pop"
}

Figure 13: Example introspection request.

7.2. AS-to-RS Response

The AS responds with a PoP token CBOR object in "application/cbor" format with
the same required and client information. The
PoP token optional parameters as in section 2.2. of RFC
7662 [RFC7662] with the following additions:

alg
OPTIONAL. See Section 6.4 for more details.

cnf
OPTIONAL. This field contains information about the public proof-of-
possession key of the client, while that binds the client
information contains to the public key access token. See
Section 6.4 for more details on the formatting of the RS. For communication
security this example uses DTLS 'cnf'
parameter.

profile
OPTIONAL. This indicates the profile that the RS MUST use with raw public keys between
the
client and client. See Section 6.4 for more details on the RS.

Note: In formatting of
this example we assume parameter.

client_token
OPTIONAL. This parameter contains information that the client knows what
resource it wants to access, and is therefore able RS MUST
pass on to request
specific audience and scope claims for the access token.

For example, Figure 7: Token Request and Response Using Client Credentials.

The information contained in the Request-Payload and 14 shows an AS response to the Response-
Payload is shown introspection
request in Figure 8.

Request-Payload : 13.

Header: Created Code=2.01)
Content-Type: "application/cbor"
Payload:
{
"grant_type" : "client_credentials",
"aud" : "tempSensorInLivingRoom",
"client_id" : "myclient",
"client_secret" : "qwerty"
}

Response-Payload
"active" :
{
"access_token" true,
"scope" : b64'SlAV32hkKG ...', "read",
"token_type" : "pop",
"csp" : "DTLS",
"key" : b64'eyJhbGciOiJSU0ExXzUi ...'
}

Figure 8: Request and Response Payload Details.

The content of the "key" parameter and the access token are shown in
Figure 9 and Figure 10.

{
"kid" : b64'c29tZSBwdWJsaWMga2V5IGlk',
"kty" : "EC",
"crv"
"alg" : "P-256",
"x" "HS256",
"profile" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4',
"y" "coap_dtls",
"client_token" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM'
}

Figure 9: Public Key b64'2QPhg0OhAQo ...
(remainder of the RS.

{
"aud" : "tempSensorInLivingRoom",
"iat" : "1360189224", client token omitted for brevity)',
"cnf" : {
"jwk"
"COSE_Key" : {
"kid" : b64'1Bg8vub9tLe1gHMzV76e8',
"kty" : "EC",
"crv" : "P-256",
"x" "Symmetric",
"kid" : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU',
"y" b64'39Gqlw',
"k" : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0' b64'hJtXhkV8FJG+Onbc6mxCcQh'
}
}
}

Figure 10: Access Token including Public Key of the Client.

Messages C and F are shown in Figure 11 - Figure 12.

C: 14: Example introspection response.

7.3. Error Response

The client then sends error responses for CoAP-based interactions with the PoP token AS are
equivalent to the /authz-info resource
at ones for HTTP-based interactions as defined in
section 2.3 of [RFC7662], with the RS. This following differences:

o If content is a plain CoAP request, i.e. no DTLS/OSCOAP
between client and RS, since sent, the token is integrity protected
between AS Content-Type MUST be set to "application/
cbor", and RS. The RS verifies that the PoP token was created
by payload MUST be encoded in a known and trusted AS, is valid, and responds to CBOR map.
o If the credentials used by the client.
The RS caches are invalid the security context together AS MUST respond
with authorization
information about this client contained in the PoP token.

The client CoAP response code code 4.01 (Unauthorized) and resource server run the DTLS handshake using use the
raw public keys established in step B
required and C.

The client sends optional parameters from section 5.2 in RFC 6749
[RFC6749].
o If the CoAP request GET to /temperature on RS over
DTLS. The RS verifies that does not have the request is authorized.

F: The RS responds with a resource representation over DTLS.

Figure 11: Access Token provisioning right to RS

Resource
Client Server
| |
|<=======>| DTLS Connection Establishment
| | using Raw Public Keys
| |
| |
+-------->| Header: GET (Code=0.01)
| GET | Uri-Path: "temperature"
| |
| |
| |
F: |<--------+ Header: 2.05 Content
| 2.05 | Payload: {"t":"22.7"}
| |

Figure 12: Resource Request and Response protected by DTLS.

6.2. Resource Server Offline

In perform this deployment scenario we consider the case of an RS that may
not be able to access introspection
request, the AS at MUST respond with the time it receives an access
request from a client. We denote CoAP response code 4.03
(Forbidden). In this case "RS offline", it involves
steps A, B, C and F of Figure 1.

If the RS no payload is offline, then it must be possible for the RS to locally
validate the access token. This requires self-contained tokens to be
used.

The validity time for the token should always be chosen as short as
possible to reduce the possibility returned.

Note that a token contains out-of-date
authorization information. Therefore the value for the Expiration
Time claim ("exp") should be set only slightly larger than the value properly formed and authorized query for the Issuing Time claim ("iss"). A constrained RS with means to
reliably measure time must validate the expiration time of the access
token.

The following example shows interactions between a client (air-
conditioning control unit), an offline resource server (temperature
sensor)and inactive or
otherwise invalid token does not warrant an authorization server. The message exchanges A and B
are shown in Figure 13.

A: The client sends error response by this
specification. In these cases, the request POST to /token at AS. The request
contains authorization server MUST instead
respond with an introspection response with the Audience parameter "active" field set to "tempSensor109797",
"false".

7.4. Client Token

EDITORIAL NOTE: We have tentatively introduced this concept and would
specifically like feedback if this is viewed as a value
that useful addition to
the temperature sensor identifies itself with. The scope framework.

In cases where the client wants the AS to authorize the access token for has limited connectivity and is "owner",
which means that the token can requesting
access to a previously unknown resource servers, using a long term
token, there are situations where it would be used beneficial to both read temperature
data and upgrade relay the firmware on the RS. The AS evaluates the
request
proof-of-possession key and authorizes other relevant information from the client AS to access
the resource.

B: The AS responds with a PoP token and client information. The
PoP token is wrapped in a COSE message, object secured content
from AS to through the RS. The client information contains a symmetric key.
In this case communication security between C and RS client_token parameter is OSCOAP
with an authenticated encryption algorithm. The client derives
two unidirectional security contexts designed to use with the resource
request
carry such information, and response messages. The access token includes the
claim "aif" with the authorized access that an owner of the
temperature device can enjoy. The "aif" claim, issued by the AS,
informs the RS that the owner of the access token, that can prove
the possession of a key is authorized intended to make a GET request
against the /tempC resource and a POST request on the /firmware
resource. be used as described in
Figure 15.

Figure 13: Token Request and Response

The information contained in the Request-Payload and the Response-
Payload is shown in Figure 14.

Request-Payload:
{
"grant_type" : "client_credentials",
"client_id" : "myclient",
"client_secret" : "qwerty",
"aud" : "tempSensor109797",
"scope" : "owner"
}

Response-Payload:
{
"access_token": b64'SlAV32hkKG ...',
"token_type" : "pop",
"csp" : "OSCOAP",
"key" : b64'eyJhbGciOiJSU0ExXzUi ...'
}

Figure 14: Request and Response Payload for RS offline

Figure 15 shows examples of the key and the access_token parameters
of the Response-Payload, decoded to CBOR.

access_token:
{
"aud" : "tempSensor109797",
"exp" : 1311281970,
"iat" : 1311280970,
"aif" : [["/tempC", 0], ["/firmware", 2]],
"cnf" : {
"ck":b64'JDLUhTMjU2IiwiY3R5Ijoi ...'
}
}

key:
{
"alg" : "AES_128_CCM_8",
"kid" : b64'U29tZSBLZXkgSWQ',
"k" : b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE'
}

Figure 15: Access Token and symmetric key from the Response-Payload

Message exchanges C and F are shown in Figure 16 and Figure 17.

C: The client then sends the PoP token to the /authz-info resource
in the RS. This is a plain CoAP request, i.e. no DTLS/OSCOAP
between client and RS, since the token is integrity protected
between AS and RS. The RS verifies that the PoP token was created
by a known and trusted AS, is valid, and responds to the client.
The RS derives and caches the security contexts together with
authorization information about this client contained in the PoP
token.

The client sends the CoAP requests GET to /tempC on the RS using
OSCOAP. The RS verifies the request and that it is authorized.

F: The RS responds with a protected status code using OSCOAP. The
client verifies the response.

Figure 16: Access Token provisioning to RS

Figure 17: Resource request and response protected by OSCOAP

In Figure 17 the GET request contains an Object-Security option and
an indication of the content 15: Use of the COSE object: a sequence number
("seq", starting from 0), client_token parameter.

The client token is a context identifier ("cid") indicating the
security context, the ciphertext COSE_Encrytped object, containing as payload a
CBOR map with the encrypted CoAP option
identifying the resource, and the Message Authentication Code ("tag")
which also covers the Code in the CoAP header.

The Object-Security ciphertext in following claims:

cnf
REQUIRED. Contains information about the response [22.7 C] represents an
encrypted temperature reading. (The COSE object is actually carried
in proof-of-possession key
the CoAP payload when possible but that is omitted to simplify
notation.)

6.3. Token Introspection with an Offline Client

In this deployment scenario we assume that a client is not be able to use with its access token. See Section 6.4.4.

token_type
OPTIONAL. See Section 6.4.2.

alg
OPTIONAL. See Section 6.4.2.

profile
REQUIRED. See Section 6.4.3.

rs_cnf
OPTIONAL. Contains information about the AS at the time of the access request. Since key that the RS is,
however, connected uses to
authenticate towards the back-end infrastructure it can make use of
token introspection. This access procedure involves steps A-F of
Figure 1, but assumes steps A and B have been carried out during a
phase when the client had connectivity to AS.

Since client. If the client key is assumed to symmetric then
this claim MUST NOT be offline, at least for a certain
period part of time, a pre-provisioned access token has to be long-lived.
The resource server may use its online connectivity to validate the
access token with the authorization server, which Client Token, since this is shown in the
example below.

In
same key as the example we show one specified through the interactions between an offline client
(key fob), a resource server (online lock), and an authorization
server. We assume that there is a provisioning step where 'cnf' claim. This claim
uses the client
has access to same encoding as the AS. This corresponds to message exchanges A and B
which are shown in Figure 18.

A: 'cnf' parameter. See Section 6.4.3.

The client sends the request AS encrypts this token using POST to /token at AS. The
request contains the Audience parameter set to "lockOfDoor4711", a
value the that key shared between the online door in question identifies itself with.
The AS generates an access token as on opaque string, which it can
match to and the specific
client, a targeted audience so that only the client can decrypt it and a symmetric access its
payload. How this key security context.

B: is established is out of scope of this
framework.

7.5. Mapping Introspection parameters to CBOR

The AS responds with the an access token introspection request and client
information, the latter containing a symmetric key. Communication
security between C response parameters are mapped to CBOR
types as follows and RS will be OSCOAP with authenticated
encryption.

Authorization
Client Server are given an integer key value to save space.

/----------------+----------+-----------------\
| Parameter name | CBOR Key | Major Type |
A: +-------->| Header: POST (Code=0.02)
|----------------+----------+-----------------|
| POST active | Uri-Path:"token" 1 | 0 (uint) | Payload: <Request-Payload>
| username |
B: |<--------+ Header: 2.05 Content 2 | 3 (text string) | Content-Type: application/cbor
| 2.05 client_id | Payload: <Response-Payload> 3 | 3 |

Figure 18: Token Request and Response using Client Credentials.

Authorization consent from the resource owner can be pre-configured,
but it can also be provided via an interactive flow with the resource
owner. An example of this for the key fob case could be that the
resource owner has a connected car, he buys a generic key that he
wants to use with the car. To authorize the key fob he connects it
to his computer that then provides the UI for the device. After that
OAuth 2.0 implicit flow is used to authorize the key for his car at
the the car manufacturers AS.

The information contained in the Request-Payload and the Response-
Payload is shown in Figure 19.

Request-Payload:
{
"grant_type" : "token",
"aud" : "lockOfDoor4711",
"client_id" : "myclient",
}

Response-Payload:
{
"access_token" : b64'SlAV32hkKG ...'
"token_type" : "pop",
"csp" : "OSCOAP",
"key" : b64'eyJhbGciOiJSU0ExXzUi ...'
}

Figure 19: Request and Response Payload for C offline

The access token in this case is just an opaque string referencing
the authorization information at the AS.

C: Next, the client POSTs the access token to the /authz-info
resource in the RS. This is a plain CoAP request, i.e. no DTLS/
OSCOAP between client and RS. Since the token is an opaque
string, the RS cannot verify it on its own, and thus defers to
respond the client with a status code until step E and only
acknowledges on the CoAP message layer (indicated with a dashed
line).

Figure 20: Access Token provisioning to RS

D: The RS forwards the token to the /introspect resource on the
AS. Introspection assumes a secure connection between the AS and
the RS, e.g. using DTLS or OSCOAP, which is not detailed in this
example.

E: The AS provides the introspection response containing claims
about the token. This includes the confirmation key (cnf) claim
that allows the RS to verify the client's proof of possession in
step F.

After receiving message E, the RS responds to the client's POST in
step C with Code 2.04 (Changed), using CoAP Token 0x2a12. This
step is not shown in the figures.

Figure 21: Token Introspection for C offline

The information contained in the Request-Payload and the Response-
Payload is shown in Figure 22.

Request-Payload:
{
"token" : b64'SlAV32hkKG...',
"client_id" : "myRS",
"client_secret" : "ytrewq"
}

Response-Payload:
{
"active" : true,
"aud" : "lockOfDoor4711",
"scope" : "open, close",
"iat" : 1311280970,
"cnf" : {
"ck" : b64'JDLUhTMjU2IiwiY3R5Ijoi ...'
}
}

Figure 22: Request and Response Payload for Introspection

The client sends the CoAP requests PUT 1 (= "close the lock") to
/lock on RS using OSCOAP with a security context derived from the
key supplied in step B. The RS verifies the request with the key
supplied in step E and that it is authorized by the token supplied
in step C.

F: The RS responds with a protected status code using OSCOAP. The
client verifies the response.

Resource
Client Server
| iss |
+-------->| Header: PUT (Code=0.03) 11 | PUT 3 | Object-Security:
| jti | (<seq>,<cid>,[Uri-Path:"lock", 1],<tag>) 12 | 3 |
F: |<--------+ Header: 2.04 Changed
| 2.04 alg | 13 | Object-Security: 3 |
| (<seq>,<cid>,,<tag>) cnf | 14 | 5 (map) |
| aud | 15 | 3 |
| client_token | 16 | 3 |
| rs_cnf | 17 | 5 |
\----------------+----------+-----------------/

Figure 23: Resource request and response protected by OSCOAP

The Object-Security ciphertext [...] of the PUT request contains CoAP
options that are encrypted, as well as the payload value '1' which is
the value of PUT 16: CBOR Mappings to Token Introspection Parameters.

8. The Access Token

This framework RECOMMENDS the door lock.

In this example there is no ciphertext use of the PUT response, but "tag"
contains a MAC which covers the request sequence number and context
identifier as well CBOR web token (CWT) as the Code which allows the Client to verify that
this actuator command was well received (door is locked).

6.4. Always-On Connectivity

A popular deployment scenario for IoT devices is to have them always
be connected to the Internet so that they can be reachable
specified in [I-D.ietf-ace-cbor-web-token].

In order to receive
commands. As a continuation from the previous scenarios we assume
that both the client and the RS are online at the time facilitate offline processing of the access
request.

If the client and the resource server are online then tokens, this
draft specfifies the AS should
be configured to issue short-lived access tokens "scope" claim for the resource to
the client. The resource server must then validate self-contained access tokens or otherwise must use token introspection to obtain the
up-to-date claim information. If transmission costs are high or the
channel is lossy, the CWT token format
[I-D.wahlstroem-ace-cbor-web-token] may be used instead of a JWT to
reduce the volume of network traffic. In terms of messaging this
deployment scenario uses the patterns described in the previous sub-
sections.

Note that despite explicitly
encodes the lack scope of connectivity constraints there may
still be other restrictions a deployment may face.

6.5. Token-less Authorization

In this deployment scenario we consider the case of an RS which is
severely energy constrained, sleeps most of the time and need to have
a tight messaging budget. It is not only infeasible to access the AS
at the time of the given access request, as in token. This claim follows the "RS offline" case
Section 6.2, it must be offloaded as much message communication
same encoding rules as
possible.

OAuth 2.0 is already an efficient protocol defined in terms of message
exchanges and can be further optimized by compact encodings section 3.3 of
tokens. [RFC6749]. The scenario illustrated in this section goes beyond that
meaning of a specific scope value is application specific and removes the access tokens from the protocol. This may
expected to be
considered a degenerate case of OAuth 2.0 but it allows us known to do two
things:

1. the RS running that application.

8.1. The common case where 'Authorization Information' Resource

The access token, containing authorization is performed by means information and
information of
authentication fits into the same protocol framework.
Authentication protocol and key is specified used by client
information, and access token is omitted.

2. Authentication, and thereby authorization, may even be implicit,
i.e. anyone with access to the right key client, is authorized transported to access
the protected resource.

In case 2., the RS does not need to receive any message from
so that the
client, and therefore enables offloading recurring resource request
and response processing to a third party, such as a Message Broker
(MB) in a publish-subscribe setting.

This scenario involves steps A, B, C and F of Figure 1 and four
parties: a client (subscriber), an offline RS (publisher), a trusted
AS, can authenticate and a MB, not necessarily trusted with access to authorize the plain text
publications. Message exchange A, B is shown in Figure 24.

A: The client sends request.
This section defines a method for transporting the request POST access token to /token at AS. The request
contains
the Audience parameter set to "birchPollenSensor301", a
value RS using CoAP that characterizes a certain pollen sensor resource. The AS
evaluates the request and authorizes MAY be used. An ACE profile MAY define other
methods for token transport.

This method REQUIRES the client RS to access the
resource.

B: The AS responds with implement an empty token and /authz-info resource. A
client information with using this method MUST make a security context POST request to be used by /authz-info on
the client. RS with the access token in the payload. The empty RS receiving the
token
signifies that authorization is performed by means MUST verify the validity of
authentication using the communication security protocol indicated
with "csp". In this case it token. If the token is object security of content (OSCON)
i.e. protection of CoAP payload only. The security context
contains valid,
the symmetric decryption key and a public signature
verification key of RS MUST respond to the RS.

Figure 24: Token Request and Response

The information contained in the Request-Payload and request with 2.04 (Changed).

If the Response-
Payload token is shown in Figure 25.

Request-Payload :
{
"grant_type" : "client_credentials",
"aud" : "birchPollenSensor301",
"client_id" : "myclient",
"client_secret" : "qwerty"
}

Response-Payload :
{
"access_token" : NULL,
"token_type" : "none",
"csp" : "OSCON",
"key" : b64'eyJhbGciOiJSU0ExXzUi ...'
}

Figure 25: Request and Response Payload for not valid, the RS severely constrained

The content of MUST respond with error code 4.01
(Unauthorized). If the "key" parameter token is shown in Figure 26.

key :
{
"alg" : "AES_128_CTR_ECDSA",
"kid" : b64'c29tZSBvdGhlciBrZXkgaWQ';
"k" : b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE',
"crv" : "P-256",
"x" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4',
"y" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM'
}

Figure 26: The 'key' Parameter

The RS, which sleeps most valid but the audience of the time, occasionally wakes up,
measures token
does not match the number birch pollens per cubic meters, publishes RS, the
measurements RS MUST respond with error code 4.03
(Forbidden).

The RS MAY make an introspection request to validate the MB, and then returns token before
responding to sleep. See Figure 27.

In this case the birch pollen count stopped at 270, which is
encrypted with POST /authz-info request. If the symmetric key and signed with introspection
response contains a client token (Section 7.4) then this token SHALL
be included in the private key payload of the RS. The MB verifies that the message originates from RS using 2.04 (Changed) response.

8.2. Token Expiration

Depending on the public key capabilities of the RS, that there are various ways in
which it is not a replay of an old measurement
using can verify the sequence number validity of the OSCON COSE profile, and caches the
object secured content. The MB does not have the secret key so is
unable to read the plain text measurement.

Message exchanges C and F are shown in Figure 27.

C: Since there is no a received access token, the client does not address token. We list
the
/authz-info resource in possibilities here including what functionality they require of
the RS.

o The client sends the CoAP request
GET to /birchPollen on MB which token is a plain CoAP request.

F: The MB responds with the cached object secured content.

Message Resource
Client Broker Server
| | |
| |<--------| Header: PUT (Code=0.02)
| | PUT | Uri-Path: "birchPollen"
| | | Payload: (<seq>,<cid>,["270"],<tag>)
| | |
| |-------->| Header: 2.04 Changed
| | 2.04 |
| |
| |
C: +-------->| Header: GET (Code=0.01)
| GET | Uri-Path: "birchPollen"
| |
| |
F: |<--------+ Header: 2.05 Content
| 2.05 | Payload: (<seq>,<cid>,["270"],<tag>)
| |

Figure 27: Sensor measurement protected by COSE

The payload is CWT/JWT and includes a COSE message consisting of sequence number 'seq'
stepped by 'exp' claim and possibly the
'nbf' claim. The RS for each publication, the context identifier 'cid' verifies these by comparing them to values
from its internal clock as defined in [RFC7519]. In this case coinciding with the key identifier 'kid'
RS must have a real time chip (RTC) or some other way of Figure 26, reliably
measuring time.
o The RS verifies the encrypted measurement and validity of the signature token by the RS.

Note that the same COSE message format may be used performing an
introspection request as specified in OSCOAP but
that only CoAP payload is protected in this case.

The authorization step is implicit, so while any client could request
access Section 7. This requires
the COSE object, only authorized clients have access RS to the
symmetric key needed have a reliable network connection to decrypt the content.

Note that in this case the order of the message exchanges A,B AS and C,F
could in principle to be interchanged, i.e. the client could first
request and obtain the protected resource
able to handle two secure sessions in steps C,F; parallel (C to RS and after
that request client information containing the keys decrypt AS to
RS).
o The RS and
verify the message.

6.6. Securing Group Communication

There are use cases that require securing communication between a
(group of) senders and AS both store a group of receivers. One prominent example sequence number linked to their
common security association. The AS increments this number for
each access token it issues and includes it in the access token,
which is lighting. Often, a set CWT/JWT. The RS keeps track of lighting nodes (e.g., luminaires, wall-
switches, sensors) are grouped together the most recently
received sequence number, and only authorized members
of accepts tokens as valid, that
are in a certain range around this number. This method does only
require the group must be able read and process messages. Additionally,
receivers of group messages must be able RS to verify the integrity keep track of
received messages as being generated within the group. sequence number. The requirements for securely communicating in such group use cases
efficiently is outlined in [I-D.somaraju-ace-multicast] along with an
architectural description method
does not provide timely expiration, but it makes sure that aligns older
tokens cease to be valid after a certain number of newer ones got
issued. For a constrained RS with the content no network connectivity and no
means of reliably measuring time, this
document. The requirements for conveying the necessary identifiers
to reference groups and also is the process of commissioning devices best that can be accomplished using the protocol described in this document. For
details about the lighting-unique use case aspects, the architecture,
as well as other multicast-specific considerations we refer the
reader to [I-D.somaraju-ace-multicast].

7.
achieved.

9. Security Considerations

The entire document is about security. Security considerations
applicable to authentication and authorization in RESTful
environments provided in OAuth 2.0 [RFC6749] apply to this work, as
well as the security considerations from [I-D.ietf-ace-actors].
Furthermore [RFC6819] provides additional security considerations for
OAuth which apply to IoT deployments as well. Finally
[I-D.ietf-oauth-pop-architecture] discusses security and privacy
threats as well as mitigation measures for Proof-of-Possession
tokens.

10. IANA Considerations

TBD

FIXME: Add

This specification registers new parameters for OAuth and establishes
registries for mappings to CBOR.

10.1. OAuth Introspection Response Parameter Registration

This specification registers the following parameters in the OAuth
introspection response parameters

o Name: "alg"
o Description: Algorithm to use with PoP key, as defined in PoP
token specification,
o Change Controller: IESG
o Specification Document(s): this document

o Name: "cnf"
o Description: Key to use to prove the right to use an access token,
as defined in [RFC7800].
o Change Controller: IESG
o Specification Document(s): this document

o Name: "aud"
o Description: reference to intended receiving RS, as defined in PoP
token specification.
o Change Controller: IESG
o Specification Document(s): this document

o Name: "profile"
o Description: The communication and communication security profile
used between client and RS, as defined in ACE profiles.
o Change Controller: IESG
o Specification Document(s): this document

o Name: "client_token"
o Description: Information that the RS MUST pass to the client e.g.
about the proof-of-possession keys.
o Change Controller: IESG
o Specification Document(s): this document

10.2. OAuth Parameter Registration

This specification registers the following parameters in the OAuth
Parameters Registry

o Name: "alg"
o Description: Algorithm to use with PoP key, as defined in PoP
token specification,
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "profile"
o Parameter usage location: token request, and token response
o Change Controller: IESG
o Specification Document(s): this document

o Name: "cnf"
o Description: Key to use to prove the right to use an access token,
as defined in [RFC7800].
o Change Controller: IESG
o Specification Document(s): this document

10.3. OAuth Access Token Types

This specification registers the following new token type in the
OAuth Access Token Types Registry

o Name: "PoP"
o Description: A proof-of-possession token.
o Change Controller: IESG
o Specification Document(s): this document

10.4. Token Type Mappings

A new registry over 'csp' values will be requested from Figure IANA, entitled "Token Type
Mappings". The registry is to be created as Expert Review Required.

10.4.1. Registration Template

Token Type:
Name of token type as registered in the OAuth token type registry
e.g. "Bearer".
Mapped value:
Integer representation for the token type value. The key value
MUST be an integer in the range of 1 to 65536.
Change Controller:

For Standards Track RFCs, list the "IESG". For others, give the
name of the responsible party. Other details (e.g., postal
address, email address, home page URI) may also be included.
Specification Document(s):
Reference to the document or documents that specify the
parameter,preferably including URIs that can be used to retrieve
copies of the documents. An indication of the relevant sections
may also be included but is not required.

10.4.2. Initial Registry Contents

o Parameter name: "Bearer"
o Mapped value: 1
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "pop"
o Mapped value: 2

FIXME: Add
o Change Controller: IESG
o Specification Document(s): this document

10.5. JSON Web Token Claims

This specification registers the following new claim in the JSON Web
Token (JWT) registry.

o Claim Name: "scope"
o Claim Description: The scope of an access token as defined in
[RFC6749].
o Change Controller: IESG
o Specification Document(s): this document

10.6. ACE Profile Registry

A new registry will be requested from IANA, entitled "ACE Profile
Registry". The registry is to be created as Expert Review Required.

10.6.1. Registration Template

Profile name:
Name of 'rpk' parameter the profile to be included in the profile attribute.
Profile description:
Text giving an over view of the profile and the context it is
developed for.
Profile ID:
Integer value to identify the profile. The value MUST be an
integer in the range of 1 to 65536.
Change Controller:

10.7. OAuth Parameter Mappings Registry

A new registry will be requested from section 5.1

FIXME: Add IANA, entitled "Token Resource
CBOR Mappings Registry". The registry is to be created as Expert
Review Required.

10.7.1. Registration Template

Parameter name:
OAuth Parameter name, refers to the name in the OAuth parameter
registry e.g. "client_id".
CBOR key value:
Key value for the claim. The key value MUST be an integer in the
range of 'tktn' values 1 to 65536.
Change Controller:
For Standards Track RFCs, list the "IESG". For others, give the
name of the responsible party. Other details (e.g., postal
address, email address, home page URI) may also be included.
Specification Document(s):
Reference to the document or documents that specify the
parameter,preferably including URIs that can be used to retrieve
copies of the documents. An indication of the relevant sections
may also be included but is not required.

10.7.2. Initial Registry Contents

o Parameter name: "client_id"
o CBOR key value: 1
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "client_secret"
o CBOR key value: 2
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "response_type"
o CBOR key value: 3
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "redirect_uri"
o CBOR key value: 4
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "scope"
o CBOR key value: 5
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "state"
o CBOR key value: 6
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "code"
o CBOR key value: 7
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "error_description"
o CBOR key value: 8
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "error_uri"
o CBOR key value: 9
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "grant_type"
o CBOR key value: 10
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "access_token"
o CBOR key value: 11
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "token_type"
o CBOR key value: 12
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "expires_in"
o CBOR key value: 13
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "username"
o CBOR key value: 14
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "password"
o CBOR key value: 15
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "refresh_token"
o CBOR key value: 16
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "alg"
o CBOR key value: 17
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "cnf"
o CBOR key value: 18
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "aud"
o CBOR key value: 19
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "profile"
o CBOR key value: 20
o Change Controller: IESG
o Specification Document(s): this document

10.8. Introspection Resource CBOR Mappings Registry

A new registry will be requested from Figure IANA, entitled "Introspection
Resource CBOR Mappings Registry". The registry is to be created as
Expert Review Required.

10.8.1. Registration Template

Response parameter name:
Name of the response parameter as defined in the "OAuth Token
Introspection Response" registry e.g. "active".
CBOR key value:
Key value for the claim. The key value MUST be an integer in the
range of 1 to 65536.
Change Controller:
For Standards Track RFCs, list the "IESG". For others, give the
name of the responsible party. Other details (e.g., postal
address, email address, home page URI) may also be included.
Specification Document(s):
Reference to the document or documents that specify the
parameter,preferably including URIs that can be used to retrieve
copies of the documents. An indication of the relevant sections
may also be included but is not required.

10.8.2. Initial Registry Contents

o Response parameter name: "active"
o CBOR key value: 1
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "username"
o CBOR key value: 2
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "client_id"
o CBOR key value: 3

8.1.
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "scope"
o CBOR key value: 4
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "token_type"
o CBOR key value: 5
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "exp"
o CBOR key value: 6
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "iat"
o CBOR key value: 7
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "nbf"
o CBOR key value: 8
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "sub"
o CBOR key value: 9
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "aud"
o CBOR key value: 10
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "iss"
o CBOR key value: 11
o Change Controller: IESG
o Specification Document(s): this document

o Response parameter name: "jti"
o CBOR key value: 12
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "alg"
o CBOR key value: 13
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "cnf"
o CBOR key value: 14
o Change Controller: IESG
o Specification Document(s): this document

o Parameter name: "aud"
o CBOR key value: 15
o Change Controller: IESG
o Specification Document(s): this document

10.9. CoAP Option Number Registration

This section registers the "Access-Token" CoAP Option Number
[RFC2046] in the
"CoRE Parameters" sub-registry "CoAP Option Numbers" in the manner
described in [RFC7252].

Name

Access-Token
Number

TBD
Reference

[draft-ietf-ace-oauth-authz]

[This document].
Meaning in Request

Contains an Access Token according to [draft-ietf-ace-oauth-authz] [This document] containing
access permissions of the client.
Meaning in Response

Not used in response
Safe-to-Forward

TBD
Format

Based on the observer the format is perseved perceived differently. Opaque
data to the client and CWT or reference token to the RS.
Length

Less then 255 bytes

11. Acknowledgments

We would like to thank Eve Maler for her contributions to the use of
OAuth 2.0 and UMA in IoT scenarios, Robert Taylor for his discussion
input, and Malisa Vucinic for his input on the ACRE proposal
[I-D.seitz-ace-core-authz] which was one source of inspiration for
this work. Finally, we would like to thank the ACE working group in
general for their feedback.

10.

Ludwig Seitz and Goeran Selander worked on this document as part of
the CelticPlus project CyberWI, with funding from Vinnova.

12. References

10.1.

12.1. Normative References

[I-D.bormann-core-ace-aif]
Bormann, C., "An Authorization Information Format (AIF)
for ACE", draft-bormann-core-ace-aif-03

[I-D.ietf-ace-cbor-web-token]
Wahlstroem, E., Jones, M., and H. Tschofenig, "CBOR Web
Token (CWT)", draft-ietf-ace-cbor-web-token-00 (work in
progress), July 2015. May 2016.

[I-D.ietf-cose-msg]
Schaad, J., "CBOR Encoded Message Syntax", draft-ietf-
cose-msg-10
cose-msg-12 (work in progress), February May 2016.

[I-D.ietf-oauth-introspection]
Richer, J., "OAuth 2.0 Token Introspection", draft-ietf-
oauth-introspection-11 (work in progress), July 2015.

[I-D.ietf-oauth-pop-architecture]
Hunt, P., Richer, J., Mills, W., Mishra, P., and H.
Tschofenig, "OAuth 2.0 Proof-of-Possession (PoP) Security
Architecture", draft-ietf-oauth-pop-architecture-07 (work
in progress), December 2015.

[I-D.ietf-oauth-pop-key-distribution]
Bradley, J., Hunt, P., Jones, M., and H. Tschofenig,
"OAuth 2.0 Proof-of-Possession: Authorization Server to
Client Key Distribution", draft-ietf-oauth-pop-key-
distribution-02 (work in progress), October 2015.

[I-D.selander-ace-object-security]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security of CoAP (OSCOAP)", draft-selander-ace-
object-security-03 (work in progress), October 2015.

[I-D.wahlstroem-ace-cbor-web-token]
Wahlstroem, E., Jones, M., and H. Tschofenig, "CBOR Web
Token (CWT)", draft-wahlstroem-ace-cbor-web-token-00 (work
in progress), December 2015.

[I-D.wahlstroem-ace-oauth-introspection]
Wahlstroem, E., "OAuth 2.0 Introspection over the
Constrained Application Protocol (CoAP)", draft-
wahlstroem-ace-oauth-introspection-01
object-security-04 (work in progress), March 2015. 2016.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC4279] Eronen, P., Ed. and H. Tschofenig, Ed., "Pre-Shared Key
Ciphersuites for Transport Layer Security (TLS)",
RFC 4279, DOI 10.17487/RFC4279, December 2005,
<http://www.rfc-editor.org/info/rfc4279>.

[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.

[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.

[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",

[RFC7662] Richer, J., Ed., "OAuth 2.0 Token Introspection",
RFC 7516, 7662, DOI 10.17487/RFC7516, May 10.17487/RFC7662, October 2015,
<http://www.rfc-editor.org/info/rfc7516>.

[RFC7517]
<http://www.rfc-editor.org/info/rfc7662>.

[RFC7800] Jones, M., "JSON Web Bradley, J., and H. Tschofenig, "Proof-of-
Possession Key (JWK)", Semantics for JSON Web Tokens (JWTs)",
RFC 7517, 7800, DOI 10.17487/RFC7517, May 2015,
<http://www.rfc-editor.org/info/rfc7517>.

10.2. 10.17487/RFC7800, April 2016,
<http://www.rfc-editor.org/info/rfc7800>.

12.2. Informative References

[I-D.ietf-ace-actors]
Gerdes, S., Seitz, L., Selander, G., and C. Bormann, "An
architecture for authorization in constrained
environments", draft-ietf-ace-actors-02 draft-ietf-ace-actors-03 (work in
progress), October 2015. March 2016.

[I-D.ietf-core-block]
Bormann, C. and Z. Shelby, "Block-wise transfers in CoAP",
draft-ietf-core-block-18
draft-ietf-core-block-20 (work in progress), April 2016.

[I-D.seitz-ace-core-authz]
Seitz, L., Selander, G., and M. Vucinic, "Authorization
for Constrained RESTful Environments", draft-seitz-ace-
core-authz-00 (work in progress), June 2015.

[I-D.somaraju-ace-multicast]
Somaraju, A., Kumar, S., Tschofenig, H., and W. Werner,
"Security for Low-Latency Group Communication", draft-
somaraju-ace-multicast-01 (work in progress), January
2016.

[RFC4680] Santesson, S., "TLS Handshake Message for Supplemental
Data", RFC 4680, DOI 10.17487/RFC4680, October 2006,
<http://www.rfc-editor.org/info/rfc4680>.

[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<http://www.rfc-editor.org/info/rfc4949>.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.

[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<http://www.rfc-editor.org/info/rfc6690>.

[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<http://www.rfc-editor.org/info/rfc6749>.

[RFC6750] Jones, M. and D. Hardt, "The OAuth 2.0 Authorization
Framework: Bearer Token Usage", RFC 6750,
DOI 10.17487/RFC6750, October 2012,
<http://www.rfc-editor.org/info/rfc6750>.

[RFC6819] Lodderstedt, T., Ed., McGloin, M., and P. Hunt, "OAuth 2.0
Threat Model and Security Considerations", RFC 6819,
DOI 10.17487/RFC6819, January 2013,
<http://www.rfc-editor.org/info/rfc6819>.

[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
October 2013, <http://www.rfc-editor.org/info/rfc7049>.

[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>.

[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.

[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.

[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<http://www.rfc-editor.org/info/rfc7519>.

[RFC7591] Richer, J., Ed., Jones, M., Bradley, J., Machulak, M., and
P. Hunt, "OAuth 2.0 Dynamic Client Registration Protocol",
RFC 7591, DOI 10.17487/RFC7591, July 2015,
<http://www.rfc-editor.org/info/rfc7591>.

[RFC7744] Seitz, L., Ed., Gerdes, S., Ed., Selander, G., Mani, M.,
and S. Kumar, "Use Cases for Authentication and
Authorization in Constrained Environments", RFC 7744,
DOI 10.17487/RFC7744, January 2016,
<http://www.rfc-editor.org/info/rfc7744>.

Appendix A. Design Justification

This section provides further insight into the design decisions of
the solution documented in this document. Section 3 lists several
building blocks and briefly summarizes their importance. The
justification for offering some of those building blocks, as opposed
to using OAuth 2.0 as is, is given below.

Common IoT constraints are:

Low Power Radio:

Many IoT devices are equipped with a small battery which needs to
last for a long time. For many constrained wireless devices the
highest energy cost is associated to transmitting or receiving
messages. It is therefore important to keep the total
communication overhead low, including minimizing the number and
size of messages sent and received, which has an impact of choice
on the message format and protocol. By using CoAP over UDP, and
CBOR encoded messages some of these aspects are addressed.
Security protocols contribute to the communication overhead and
can in some cases be optimized. For example authentication and
key establishment may in certain cases where security requirements
so allows be replaced by provisioning of security context by a
trusted third party, using transport or application layer
security.

Low CPU Speed:

Some IoT devices are equipped with processors that are
significantly slower than those found in most current devices on
the Internet. This typically has implications on what timely
cryptographic operations a device is capable to perform, which in
turn impacts e.g. protocol latency. Symmetric key cryptography
may be used instead of the computationally more expensive public
key cryptography where the security requirements so allows, but
this may also require support for trusted third party assisted
secret key establishment using transport or application layer
security.

Small Amount of Memory:

Microcontrollers embedded in IoT devices are often equipped with
small amount of RAM and flash memory, which places limitations
what kind of processing can be performed and how much code can be
put on those devices. To reduce code size fewer and smaller
protocol implementations can be put on the firmware of such a
device. In this case, CoAP may be used instead of HTTP, symmetric
key cryptography instead of public key cryptography, and CBOR
instead of JSON. Authentication and key establishment protocol,
e.g. the DTLS handshake, in comparison with assisted key
establishment also has an impact on memory and code.

User Interface Limitations:

Protecting access to resources is both an important security as
well as privacy feature. End users and enterprise customers do
not want to give access to the data collected by their IoT device
or to functions it may offer to third parties. Since the
classical approach of requesting permissions from end users via a
rich user interface does not work in many IoT deployment scenarios
these functions need to be delegated to user controlled devices
that are better suitable for such tasks, such as smart phones and
tablets.
Communication Constraints:

In certain constrained settings an IoT device may not be able to
communicate with a given device at all times. Devices may be
sleeping, or just disconnected from the Internet because of
general lack of connectivity in the area, for cost reasons, or for
security reasons, e.g. to avoid an entry point for Denial-of-
Service attacks.

The communication interactions this framework builds upon (as
shown graphically in Figure 1) may be accomplished using a variety
of different protocols, and not all parts of the message flow are
used in all applications due to the communication constraints.
While we envision deployments to make use of CoAP we explicitly
want to support HTTP, HTTP/2 or specific protocols, such as
Bluetooth Smart communication, which does not necessarily use IP.
The latter raises the need for application layer security over the
various interfaces.

Appendix B. Roles and Responsibilites -- a Checklist

Resource Owner

* Make sure that the RS is registered at the AS.
* Make sure that clients can discover the AS which is in charge
of the RS.
* Make sure that the AS has the necessary, up-to-date, access
control policies for the RS.

Requesting Party

* Make sure that the client is provisioned the necessary
credentials to authenticate to the AS.
* Make sure that the client is configured to follow the security
requirements of the Requesting Party, when issuing requests
(e.g. minimum communication security requirements, trust
anchors).
* Register the client at the AS.

Authorization Server

* Register RS and manage corresponding security contexts.
* Register clients and including authentication credentials.
* Allow Resource Onwers Owners to configure and update access control
policies related to their registered RS'
* Expose a service that allows clients to request tokens.
* Authenticate clients that wishes to request a token.
* Process a token requests against the authorization policies
configured for the RS.
* Expose a service that allows RS's to submit token introspection
requests.
* Authenticate RS's that wishes to get an introspection response.
* Process token introspection requests.
* Optionally: Handle token revocation.

Client

* Discover the AS in charge of the RS that is to be targeted with
a request.
* Submit the token request (A).

+ Authenticate towards the AS.
+ Specify which RS, which resource(s), and which action(s) the
request(s) will target.
+ Specify preferences for communication security
+ If raw public key (rpk) or certificate is used, make sure
the AS has the right rpk or certificate for this client.
* Process the access token and client information (B)

+ Check that the token has the right format (e.g. CWT).
+ Check that the client information provides the necessary
security parameters (e.g. PoP key, information on
communication security protocols supported by the RS).
* Send the token and request to the RS (C)

+ Authenticate towards the RS (this could coincide with the
proof of possession process).
+ Transmit the token as specified by the AS (default is to an
authorization information resource, alternative options are
as a CoAP option or in the DTLS handshake).
+ Perform the proof-of-possession procedure as specified for
the type of used token (this may already have been taken
care of through the authentication procedure).
* Process the RS response (F) requirements of the Requesting
Party, when issuing requests (e.g. minimum communication
security requirements, trust anchors).
* Register the client at the AS.

Resource Server

* Expose a way to submit access tokens.
* Process an access token.

+ Verify the token is from the right AS.
+ Verify that the token applies to this RS.
+ Check that the token has not expired (if the token provides
expiration information).
+ Check the token's integrity.
+ Store the token so that it can be retrieved in the context
of a matching request.
* Process a request.

+ Set up communication security with the client.

+ Authenticate the client.
+ Match the client against existing tokens.
+ Check that tokens belonging to the client actually authorize
the requested action.
+ Optionally: Check that the matching tokens are still valid
(if this is possible.
* Send a response following the agreed upon communication
security.

Appendix C. Optimizations Deployment Examples

There is a large variety of IoT deployments, as is indicated in
Appendix A, and this section highlights a few common variants. This
section sketches some potential optimizations to the presented
solution.

Access token in DTLS handshake

In is not normative but illustrates how the case framework can be
applied.

For each of CSP=DTLS/TLS, the access token provisioning
exchange deployment variants there are a number of possible
security setups between clients, resource servers and authorization
servers. The main focus in step C the following subsections is on how
authorization of a client request for a resource hosted by a RS is
performed. This requires the protocol may be embedded in the security
handshake. Different solutions are possible, where one
standardized method would be the use of the TLS supplemental data
extension [RFC4680] for transferring requests and
responses between the access token.

Reference token clients and introspection the RS to consider.

Note: CBOR diagnostic notation is used for examples of requests and
responses.

C.1. Local Token Validation

In this scenario we consider the case of introspection where the resource server is
offline, i.e. it may is not connected to the AS at the time of the access
request. This access procedure involves steps A, B, C, and F of
Figure 1.

Since the resource server must be beneficial able to utilize verify the access
tokens which are not token
locally, self-contained (also known access tokens must be used.

This example shows the interactions between a client, the
authorization server and a temperature sensor acting as "reference
tokens") that a resource
server. Message exchanges A and B are shown in Figure 17.

A: The client first generates a public-private key pair used for
communication security with the RS.
The client sends the POST request to lookup detailed information about /token at the
authorization. AS. The RS uses
request contains the introspection message exchange not
only for validating token claims, but also for obtaining claims public key of the client and the Audience
parameter set to "tempSensorInLivingRoom", a value that potentially were not known at the time when
temperature sensor identifies itself with. The AS evaluates the
request and authorizes the client to access the resource.

B: The AS responds with a PoP token
was issued.

A reference and client information. The
PoP token can be made much more compact than a self-
contained token, since it does not need to contain any contains the public key of claims
that it represents. This could be very useful in particular if the client is constrained client, and offline most the client
information contains the public key of the time.

Reference RS. For communication
security this example uses DTLS RawPublicKey between the client
and the RS. The issued token in CoAP option

While large access will have a short validity time,
i.e. 'exp' close to 'iat', to protect the RS from replay attacks
since it, that cannot do introspection to check the tokens must be sent in CoAP payload, if current
validity. The token includes the claim "aif" with the authorized
access token is known to be that an owner of a certain limited size, for example
in the case temperature device can enjoy. The
'aif' claim, issued by the AS, informs the RS that the owner of a reference
the token, then it would be favorable to
combine that can prove the access token provisioning possession of a key is authorized to
make a GET request with against the /temperature resource and a POST
request to on the RS.

One way to achieve /firmware resource.
Note: In this example we assume that the client knows what
resource it wants to access, and is therefore able to define a new CoAP option request
specific audience and scope claims for
carrying reference tokens, called "Ref-Token" as shown in the
example in Figure 28.

Resource access token.

Figure 28: Reference 17: Token Request and Response Using Client Credentials.

The information contained in CoAP Option

Appendix D. CoAP the Request-Payload and CBOR profiles for OAuth 2.0

Many IoT devices can support OAuth 2.0 without any additional
extensions, but for certain constrained settings additional profiling the Response-
Payload is needed. In this appendix we define CoAP resources for shown in Figure 18.

Request-Payload :
{
"grant_type" : "client_credentials",
"aud" : "tempSensorInLivingRoom",
"client_id" : "myclient",
"client_secret" : "qwerty"
}

Response-Payload :
{
"access_token" : b64'SlAV32hkKG ...',
"token_type" : "pop",
"csp" : "DTLS",
"cnf" : {
"COSE_Key" : {
"kid" : b64'c29tZSBwdWJsaWMga2V5IGlk',
"kty" : "EC",
"crv" : "P-256",
"x" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4',
"y" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM'
}
}
}

Figure 18: Request and Response Payload Details.

The content of the HTTP
based access token and introspection endpoints used is shown in vanilla OAuth 2.0.
We also define a CBOR alternative to Figure 19.

{
"aud" : "tempSensorInLivingRoom",
"iat" : "1360189224",
"exp" : "1360289224",
"aif" : [["/temperature", 0], ["/firmware", 2]],
"cnf" : {
"jwk" : {
"kid" : b64'1Bg8vub9tLe1gHMzV76e8',
"kty" : "EC",
"crv" : "P-256",
"x" : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU',
"y" : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0'
}
}
}

Figure 19: Access Token including Public Key of the JSON Client.

Messages C and form based POST
structures used F are shown in HTTP.

D.1. Profile for Token resource Figure 20 - Figure 21.

C: The token resource is used by the client to obtain an access then sends the PoP token by
presenting its authorization grant or client credentials to the
/token /authz-info resource
at the AS.

D.1.1. Token Request

The client makes a request to the token resource by sending RS. This is a CBOR
structure with the following attributes.

grant_type:

REQUIRED. The grant type, "code", "client_credentials",
"password" plain CoAP request, i.e. no transport or others.

client_id:

OPTIONAL. The
application layer security between client identifier issued to the holder of and RS, since the token
(client or RS) during the registration process.

client_secret:

OPTIONAL. The client secret.

scope:

OPTIONAL.
is integrity protected between AS and RS. The scope of RS verifies that
the access request as described PoP token was created by
Section 3.1.

aud:

OPTIONAL. Service-specific string identifier or list of string
identifiers representing a known and trusted AS, is valid, and
responds to the intended audience for this token, as
defined in [I-D.wahlstroem-ace-cbor-web-token].

alg:

OPTIONAL. client. The value in RS caches the 'alg' parameter security context
together with value
from the 'token_type' parameter allow the client to indicate the
supported algorithms for a given token type.

key:

OPTIONAL. This field contains authorization information about the public key
the this client would like to bind to the access token
contained in the COSE Key
Structure format.

The parameters defined above use the following CBOR major types.

/-----------+--------------+-----------------------\
| Value | Major Type PoP token.

Resource
Client Server
| Key |
|-----------+--------------+-----------------------|
C: +-------->| Header: POST (Code=0.02)
| 0 POST | 0 Uri-Path:"authz-info"
| grant_type | Payload: SlAV32hkKG ...
| 1 | 0
|<--------+ Header: 2.01 Created
| client_id 2.01 |
| 2 | 0

Figure 20: Access Token provisioning to RS
The client and the RS runs the DTLS handshake using the raw public
keys established in step B and C.
The client sends the CoAP request GET to /temperature on RS over
DTLS. The RS verifies that the request is authorized, based on
previously established security context.
F: The RS responds with a resource representation over DTLS.

Resource
Client Server
| client_secret |
|<=======>| DTLS Connection Establishment
| 3 | 0 using Raw Public Keys
| scope |
+-------->| Header: GET (Code=0.01)
| 4 GET | 0 Uri-Path: "temperature"
| aud |
| 5 | 0
| alg |
F: |<--------+ Header: 2.05 Content
| 6 2.05 | 0 Payload: <sensor value>
| key |
\-----------+--------------+-----------------------/

Figure 29: CBOR mappings used in token requests

D.1.2. Token 21: Resource Request and Response

The AS responds protected by sending DTLS.

C.2. Introspection Aided Token Validation

In this deployment scenario we assume that a CBOR structure with the following
attributes.

access_token:

REQUIRED. The client is not be able to
access token issued by the authorization server.

token_type:

REQUIRED. The type AS at the time of the token issued. "pop" is recommended.

key:

REQUIRED, if symmetric key cryptography is used. A COSE Key
Structure containing access request. Since the symmetric proof RS is,
however, connected to the back-end infrastructure it can make use of possession key. The
members
token introspection. This access procedure involves steps A-F of
Figure 1, but assumes steps A and B have been carried out during a
phase when the structure can client had connectivity to AS.

Since the client is assumed to be found in section 7.1 offline, at least for a certain
period of
[I-D.ietf-cose-msg].

csp:

REQUIRED. Information on what communication protocol time, a pre-provisioned access token has to be long-lived.
The resource server may use its online connectivity to validate the
access token with the authorization server, which is shown in the communication
example below.

In the example we show the interactions between an offline client
(key fob), a resource server (online lock), and an authorization
server. We assume that there is a provisioning step where the client
has access to the AS. This corresponds to message exchanges A and B
which are shown in Figure 22.

Authorization consent from the RS. Details on
possible values resource owner can be found in Section 5.1.

scope:

OPTIONAL, if identical to pre-configured,
but it can also be provided via an interactive flow with the scope requested by resource
owner. An example of this for the client;
otherwise, REQUIRED.

alg:

OPTIONAL. The 'alg' parameter provides further information about key fob case could be that the algorithm, such as whether
resource owner has a symmetric or an asymmetric
crypto-system is used.

The parameters defined above connected car, he buys a generic key that he
wants to use with the car. To authorize the following CBOR major types.

/-----------+--------------+-----------------------\
| Value | Major Type | Key |
|-----------+--------------+-----------------------|
| 0 | 0 | access_token |
| 1 | 0 | token_type |
| 2 | 0 | key |
| 3 | 0 | csp |
| 4 | 0 | scope |
| 5 | 0 | alg |
\-----------+--------------+-----------------------/

Figure 30: CBOR mappings used in token responses

D.2. CoAP Profile fob he connects it
to his computer that then provides the UI for the device. After that
OAuth Introspection

This section defines a way 2.0 implicit flow can used to authorize the key for a holder of access tokens, mainly
clients and RS's, his car at
the the car manufacturers AS.

Note: In this example the client does not know the exact door it will
be used to get metadata like validity status, claims and
scopes found in access token. The OAuth Token Introspection
specification [I-D.ietf-oauth-introspection] defines a way to
validate since the token using HTTP POST or HTTP GET. This document reuses
the work done in request is not send at the OAuth Token Introspection and defines a mapping time of
access. So the request scope and response to CoAP [RFC7252] audience parameters is set quite wide to
start with and new values different form the original once can be used by
constrained devices.

D.2.1. Introspection Request
returned from introspection later on.

A: The token holder makes a client sends the request using POST to /token at AS. The
request contains the Introspection CoAP resource
by sending Audience parameter set to "PACS1337" (PACS,
Physical Access System), a CBOR structure with the following attributes.

token:

REQUIRED. The string value of the token.

resource_id:

OPTIONAL. A service-specific string identifying the resource that the client doing the introspection is asking about.

client_id:

OPTIONAL. online door in
question identifies itself with. The client identifier issued AS generates an access token
as on opaque string, which it can match to the holder of specific client, a
targeted audience and a symmetric key.
B: The AS responds with the an access token
(client or RS) during the registration process.

client_secret:

OPTIONAL. The and client secret.
information, the latter containing a symmetric key. Communication
security between C and RS will be DTLS and PreSharedKey. The parameters defined above use PoP
key being used as the following CBOR major types:

/-----------+--------------+-----------------------\
| Value | Major Type PreSharedKey.

Authorization
Client Server
| Key |
|-----------+--------------+-----------------------|
| 0 | 0
A: +-------->| Header: POST (Code=0.02)
| token POST | Uri-Path:"token"
| 1 | 0 Content-Type: application/cbor
| resource_id | Payload: <Request-Payload>
| 2 | 0
B: |<--------+ Header: 2.05 Content
| client_id | Content-Type: application/cbor
| 3 2.05 | 0 Payload: <Response-Payload>
| client_secret |
\-----------+--------------+-----------------------/

Figure 31: CBOR Mappings to 22: Token Introspection Request Parameters.

D.2.2. Introspection and Response

If using Client Credentials.

The information contained in the introspection request is valid Request-Payload and authorized, the
authorization server returns a CoAP message with the response encoded
as a CBOR structure Response-
Payload is shown in the payload of the message. If the request
failed client authentication or Figure 23.

Request-Payload:
{
"grant_type" : "client_credentials",
"aud" : "lockOfDoor4711",
"client_id" : "keyfob",
"client_secret" : "qwerty"
}

Response-Payload:
{
"access_token" : b64'SlAV32hkKG ...'
"token_type" : "pop",
"csp" : "DTLS",
"cnf" : {
"COSE_Key" : {
"kid" : b64'c29tZSBwdWJsaWMga2V5IGlk',
"kty" : "oct",
"alg" : "HS256",
"k": b64'ZoRSOrFzN_FzUA5XKMYoVHyzff5oRJxl-IXRtztJ6uE'
}
}
}

Figure 23: Request and Response Payload for C offline

The access token in this case is invalid, just an opaque string referencing
the authorization server
returns an error response using information at the CoAP 4.00 'Bad Request' response
code.

The JSON structure in AS.

C: Next, the payload response includes client POSTs the top-level
members defined in Section 2.2 access token to the /authz-info
resource in the OAuth Token Introspection
specification [I-D.ietf-oauth-introspection]. It RS. This is RECOMMENDED to
only return the 'active' attribute considering constrained nature of a plain CoAP request, i.e. no DTLS
between client and server networks.

Introspection responses in CBOR use the following mappings:

active:

REQUIRED. The active key is an indicator of whether or not RS. Since the
presented token is currently active. The specifics of a token's
"active" state will vary depending on the implementation of the
authorization server, and an opaque string, the information
RS cannot verify it keeps about on its
tokens, but a "true" value return for own, and thus defers to respond the "active" property will
generally indicate that
client with a given token has been issued by this
authorization server, has not been revoked by the resource owner,
and is within its given time window of validity (e.g., status code until after its
issuance time and before its expiration time).

scope:

OPTIONAL. A string containing a space-separated list of scopes
associated with this token, in the format described in Section 3.3
of OAuth 2.0 [RFC6749].

client_id:

OPTIONAL. Client identifier for step E.
D: The RS forwards the client that requested this
token.

username:

OPTIONAL. Human-readable identifier for token to the /introspect resource owner who
authorized this token.

token_type:

OPTIONAL. Type of on the token as defined in Section 5.1 of OAuth
2.0 [RFC6749] or PoP token.

exp:

OPTIONAL. Integer timestamp, measured in
AS. Introspection assumes a secure connection between the number of seconds
since January 1 1970 UTC, indicating when this token will expire,
as defined in CWT [I-D.wahlstroem-ace-cbor-web-token].

iat:

OPTIONAL. Integer timestamp, measured in AS and
the number RS, e.g. using transport of seconds
since January 1 1970 UTC, indicating when this token will expire,
as defined in CWT [I-D.wahlstroem-ace-cbor-web-token].

nbf:

OPTIONAL. Integer timestamp, measured application layer security, which
is not detailed in the number of seconds
since January 1 1970 UTC, indicating when this token will expire,
as defined in CWT [I-D.wahlstroem-ace-cbor-web-token].

sub:

OPTIONAL. Subject of example.
E: The AS provides the token, as defined in CWT
[I-D.wahlstroem-ace-cbor-web-token]. Usually a machine-readable
identifier of introspection response containing
parameters about the resource owner who authorized this token.

aud:

OPTIONAL. Service-specific string identifier or list of string
identifiers representing This includes the intended audience for this token, as
defined in CWT [I-D.wahlstroem-ace-cbor-web-token].

iss:

OPTIONAL. String representing confirmation key
(cnf) parameter that allows the RS to verify the issuer client's proof of this token, as
defined
possession in CWT [I-D.wahlstroem-ace-cbor-web-token].

cti:

OPTIONAL. String identifier for step F.
After receiving message E, the token, as defined in CWT
[I-D.wahlstroem-ace-cbor-web-token]

The parameters defined above use RS responds to the following CBOR major types:

/-----------+--------------+-----------------------\ client's POST in
step C with Code 2.01 Created.

Resource
Client Server
| Value | Major Type
C: +-------->| Header: POST (T=CON, Code=0.02)
| Key POST |
|-----------+--------------+-----------------------| Uri-Path:"authz-info"
| 0 | 0 Content-Type: "application/cbor"
| active | Payload: b64'SlAV32hkKG ...''
| 1 | 0
| scopes | Authorization
| 2 | 0 Server
| client_id | | 3
D: | 0 +--------->| Header: POST (Code=0.02)
| username | POST | 4 Uri-Path: "introspect"
| 0 | token_type | Content-Type: "application/cbor"
| 5 | 0 | exp Payload: <Request-Payload>
| | 6 | 0
E: | iat |<---------+ Header: 2.05 Content
| | 7 2.05 | 0 Content-Type: "application/cbor"
| nbf | | 8 Payload: <Response-Payload>
| 0 | sub |
| 9 | 0
C: |<--------+ Header: 2.01 Created
| aud 2.01 |
| 10 | 0

Figure 24: Token Introspection for C offline
The information contained in the Request-Payload and the Response-
Payload is shown in Figure 25.

Request-Payload:
{
"token" : b64'SlAV32hkKG...',
"client_id" : "FrontDoor",
"client_secret" : "ytrewq"
}

Response-Payload:
{
"active" : true,
"aud" : "lockOfDoor4711",
"scope" : "open, close",
"iat" : 1311280970,
"cnf" : {
"kid" : b64'JDLUhTMjU2IiwiY3R5Ijoi ...'
}
}

Figure 25: Request and Response Payload for Introspection

The client uses the symmetric PoP key to establish a DTLS
PreSharedKey secure connection to the RS. The CoAP request PUT is
sent to the uri-path /state on RS changing state of the door to
locked.
F: The RS responds with a appropriate over the secure DTLS
channel.

Resource
Client Server
| iss |
|<=======>| DTLS Connection Establishment
| | 11 using Pre Shared Key
| 0 | cti
+-------->| Header: PUT (Code=0.03)
| PUT | Uri-Path: "state"
| | Payload: <new state for the lock>
| |
F: |<--------+ Header: 2.04 Changed
| 2.04 | Payload: <new state for the lock>
| |
\-----------+--------------+-----------------------/

Figure 32: CBOR Mappings to Token Introspection Response Parameters. 26: Resource request and response protected by OSCOAP

Appendix E. D. Document Updates

E.1.
D.1. Version -01 to -02

o Restructured to remove communication security parts. These shall
now be defined in profiles.
o Restructured section 5 to create new sections on the OAuth
endpoints /token, /introspect and /authz-info.
o Pulled in material from draft-ietf-oauth-pop-key-distribution in
order to define proof-of-possession key distribution.
o Introduced the 'cnf' parameter as defined in RFC7800 to reference
or transport keys used for proof of posession.
o Introduced the 'client-token' to transport client information from
the AS to the client via the RS in conjunction with introspection.
o Expanded the IANA section to define parameters for token request,
introspection and CWT claims.
o Moved deployment scenarios to the appendix as examples.

D.2. Version -00 to -01

o Changed 5.1. from "Communication Security Protocol" to "Client
Information".
o Major rewrite of 5.1 to clarify the information exchanged between
C and AS in the PoP token request profile for IoT.

* Allow the client to indicate preferences for the communication
security protocol.
* Defined the term "Client Information" for the additional
information returned to the client in addition to the access
token.
* Require that the messages between AS and client are secured,
either with (D)TLS or with COSE_Encrypted wrappers.
* Removed dependency on OSCoAP and added generic text about
object security instead.
* Defined the "rpk" parameter in the client information to
transmit the raw public key of the RS from AS to client.
* (D)TLS MUST use the PoP key in the handshake (either as PSK or
as client RPK with client authentication).
* Defined the use of x5c, x5t and x5tS256 parameters when a
client certificate is used for proof of possession.
* Defined "tktn" parameter for signaling for how to tranfer transfer the
access token.
o Added 5.2. the CoAP Access-Token option for transfering transferring access
tokens in messages that do not have payload.
o 5.3.2. Defined success and error responses from the RS when
receiving an access token.
o 5.6.:Added section giving guidance on how to handle token
expiration in the absence of reliable time.
o Appendix B Added list of roles and responsibilities for C, AS and
RS.

Authors' Addresses

Ludwig Seitz
SICS
Scheelevaegen 17
Lund 223 70
SWEDEN

Email: ludwig@sics.se

Goeran Selander
Ericsson
Faroegatan 6
Kista 164 80
SWEDEN

Email: goran.selander@ericsson.com

Erik Wahlstroem
Nexus Technology
Telefonvagen 26
Hagersten 126 26
Sweden

Email: erik.wahlstrom@nexusgroup.com

Samuel Erdtman
Nexus Technology
Telefonvagen 26
Hagersten 126 26
Spotify AB
Birger Jarlsgatan 61, 4tr
Stockholm 113 56
Sweden

Email: samuel.erdtman@nexusgroup.com erdtman@spotify.com

Hannes Tschofenig
ARM Ltd.
Hall in Tirol 6060
Austria

Email: Hannes.Tschofenig@arm.com