Authorization for the Internet of Things using OAuth 2.0
draft-ietf-ace-oauth-authz-01
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9200.
|
|
|---|---|---|---|
| Authors | Ludwig Seitz , Göran Selander , Erik Wahlstroem , Samuel Erdtman , Hannes Tschofenig | ||
| Last updated | 2016-06-01 (Latest revision 2016-02-25) | ||
| Replaces | draft-seitz-ace-oauth-authz, draft-tschofenig-ace-oauth-iot, draft-tschofenig-ace-oauth-bt | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
GENART Last Call review
(of
-27)
by Stewart Bryant
Ready w/nits
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Kepeng Li | ||
| IESG | IESG state | Became RFC 9200 (Proposed Standard) | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | "Kepeng Li" <kepeng.lkp@alibaba-inc.com> |
draft-ietf-ace-oauth-authz-01
ACE Working Group L. Seitz
Internet-Draft SICS
Intended status: Standards Track G. Selander
Expires: August 28, 2016 Ericsson
E. Wahlstroem
S. Erdtman
Nexus Technology
H. Tschofenig
ARM Ltd.
February 25, 2016
Authorization for the Internet of Things using OAuth 2.0
draft-ietf-ace-oauth-authz-01
Abstract
This memo defines how to use OAuth 2.0 as an authorization framework
with Internet of Things (IoT) deployments, thus bringing a well-known
and widely used security solution to IoT devices. Where possible
vanilla OAuth 2.0 is used, but where the limitations of IoT devices
require it, profiles and extensions are provided.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 28, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. OAuth 2.0 . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. CoAP . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Object Security . . . . . . . . . . . . . . . . . . . . . 8
4. Protocol Interactions . . . . . . . . . . . . . . . . . . . . 9
5. OAuth 2.0 Profiling . . . . . . . . . . . . . . . . . . . . . 12
5.1. Client Information . . . . . . . . . . . . . . . . . . . 12
5.2. CoAP Access-Token Option . . . . . . . . . . . . . . . . 15
5.3. Authorization Information Resource at the Resource Server 15
5.3.1. Authorization Information Request . . . . . . . . . . 16
5.3.2. Authorization Information Response . . . . . . . . . 16
5.3.2.1. Success Response . . . . . . . . . . . . . . . . 16
5.3.2.2. Error Response . . . . . . . . . . . . . . . . . 16
5.4. Authorization Information Format . . . . . . . . . . . . 17
5.5. CBOR Data Formats . . . . . . . . . . . . . . . . . . . . 17
5.6. Token Expiration . . . . . . . . . . . . . . . . . . . . 17
6. Deployment Scenarios . . . . . . . . . . . . . . . . . . . . 18
6.1. Client and Resource Server are Offline . . . . . . . . . 19
6.2. Resource Server Offline . . . . . . . . . . . . . . . . . 22
6.3. Token Introspection with an Offline Client . . . . . . . 26
6.4. Always-On Connectivity . . . . . . . . . . . . . . . . . 30
6.5. Token-less Authorization . . . . . . . . . . . . . . . . 31
6.6. Securing Group Communication . . . . . . . . . . . . . . 34
7. Security Considerations . . . . . . . . . . . . . . . . . . . 35
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
8.1. CoAP Option Number Registration . . . . . . . . . . . . . 35
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 36
10.1. Normative References . . . . . . . . . . . . . . . . . . 36
10.2. Informative References . . . . . . . . . . . . . . . . . 38
Appendix A. Design Justification . . . . . . . . . . . . . . . . 40
Appendix B. Roles and Responsibilites -- a Checklist . . . 41
Appendix C. Optimizations . . . . . . . . . . . . . . . . . . . 44
Appendix D. CoAP and CBOR profiles for OAuth 2.0 . . . . . . . . 45
D.1. Profile for Token resource . . . . . . . . . . . . . . . 45
D.1.1. Token Request . . . . . . . . . . . . . . . . . . . . 46
D.1.2. Token Response . . . . . . . . . . . . . . . . . . . 47
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D.2. CoAP Profile for OAuth Introspection . . . . . . . . . . 48
D.2.1. Introspection Request . . . . . . . . . . . . . . . . 48
D.2.2. Introspection Response . . . . . . . . . . . . . . . 49
Appendix E. Document Updates . . . . . . . . . . . . . . . . . . 51
E.1. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52
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 authorization task can 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.
We envision that end consumers and enterprises will want to manage
access-control and authorization for their Internet of Things (IoT)
devices in the same style and this desire will increase with the
number of exposed services and capabilities provided by applications
hosted on the IoT devices. The IoT devices may be constrained in
various ways including processing, memory, code-size, energy, etc.,
as defined 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, and all levels in between.
Thus IoT devices are very different in terms of available processing
and message exchange capabilities.
This memo describes how to re-use OAuth 2.0 [RFC6749] to extend
authorization to Internet of Things devices with different kinds of
constraints. At the time of writing, OAuth 2.0 is already used with
certain types of IoT devices and this document will provide
implementers additional guidance for using it in a secure and
privacy-friendly way. Where possible the basic OAuth 2.0 mechanisms
are used; in some circumstances profiles are defined, for example to
support smaller the over-the-wire message size and smaller code size.
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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 the term
"endpoint" to denote HTTP resources such as /token and /authorize at
the AS, but we will use the term "resource" in this memo to avoid
confusion with the CoAP [RFC7252] term "endpoint".
Since this draft 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 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 be
provided either by DTLS 1.2 [RFC6347] or TLS 1.2 [RFC5246].
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 and this
document defines such an alternative encoding. The COSE message
format [I-D.ietf-cose-msg] is also based on CBOR.
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A fourth building block is application layer security, which is used
where transport layer security is insufficient. At the time of
writing the preferred approach for securing CoAP at the application
layer is via the use of COSE [I-D.ietf-cose-msg], which adds object
security to CBOR-encoded data. More details about applying COSE to
CoAP can be found in 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 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 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 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:
Access Tokens:
Access tokens are credentials used to access protected resources.
An access token is a data structure representing authorization
permissions issued to the client. Access tokens are generated by
the authorization server and consumed by the resource server. The
access token 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.
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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 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.
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 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:
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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" 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 uses CBOR encoded
messages defined in Appendix D 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 carried in the access token in the form of type-
value pairs is called claims. An access token may for example
include a claim about the AS that issued the token (the "iss"
claim) and what audience the access token is intended for (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] 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].
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.
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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 does not allow the fragmentation 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 be provided. COSE [I-D.ietf-cose-msg] defines
a message format for cryptographic protection of data using CBOR
encoding. There are two main approaches for application layer
security:
Object Security of CoAP (OSCOAP)
OSCOAP [I-D.selander-ace-object-security] is a method for
protecting CoAP request/response message exchanges, including CoAP
payloads, CoAP header fields as well as CoAP options. OSCOAP
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 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 are that an OSCON message can be passed across
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different protocols, from request to response, and used to secure
group communications.
4. Protocol Interactions
This framework is based on the same protocol interactions as OAuth
2.0: A client obtains an access token from an AS and presents the
token to an RS to gain access to a protected resource. 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 (= client owner) are not shown in Figure 1.
For the description in this document we assume that the client has
been registered to an AS. Registration means that the two share
credentials, configuration parameters and that some form of
authorization has taken place. These credentials are used to protect
the token request by the client and the transport of access tokens
and client information from AS to the client.
It is also assumed that the RS 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 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 on the protocols being used and the specific
deployment environment. In Bluetooth Smart, for example,
advertisements are broadcasted by a peripheral, including information
about the supported 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].
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+--------+ +---------------+
| |---(A)-- Token Request ------------->| |
| | | Authorization |
| |<--(B)-- Access Token ---------------| Server |
| | + Client Information | |
| | +---------------+
| | ^ |
| | Introspection Request & Response (D)| |(E)
| Client | | v
| | +--------------+
| |---(C)-- Token + Request ----------->| |
| | | Resource |
| |<--(F)-- Protected Resource ---------| Server |
| | | |
+--------+ +--------------+
Figure 1: Overview of the basic protocol flow
Requesting an Access Token (A):
The client makes an access token request to the AS. This memo
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 or
asymmetric cryptography).
Access Token Response (B):
If the AS successfully processes the request from the client, it
returns an access token. It also includes various parameters,
which we call "Client Information". In addition to the response
parameters defined by OAuth 2.0 and the PoP token extension, we
consider new kinds of response parameters in Section 5, including
information on which security protocol 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 information as described in
Section 5.1.
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; HTTP,
HTTP/2, Bluetooth Smart etc., are also possible candidates.
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Depending on the device limitations and the selected protocol this
exchange may be split up into two phases:
(1) the client sends the access token to a newly defined
authorization endpoint at the RS (see Section 5.3) , which
conveys authorization information to the RS that may be used by
the client for subsequent resource requests, and
(2) the client makes the resource access request, using the
communication security protocol and other client information
obtained from the AS.
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 the AS to obtain the most recent claims, such as
scope, audience, validity etc. associated with a specific access
token. Token introspection over CoAP is defined in
[I-D.wahlstroem-ace-oauth-introspection] and for HTTP in
[I-D.ietf-oauth-introspection].
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 associated with
it back to the RS. The RS then uses the received claims to
process the request to either accept or to deny it.
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.
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5. OAuth 2.0 Profiling
This section describes profiles of OAuth 2.0 adjusting it to
constrained environments for use cases where this is necessary.
Profiling for JSON Web Tokens (JWT) is provided in
[I-D.wahlstroem-ace-cbor-web-token].
5.1. Client Information
OAuth 2.0 using bearer tokens, as described in [RFC6749] and in
[RFC6750], requires TLS for all communication interactions between
client, authorization server, and resource server. This is possible
in the scope where OAuth 2.0 was originally developed: web and mobile
applications. In these environments resources like computational
power and bandwidth are not scarce and operating systems as well as
browser platforms are pre-provisioned with trust anchors 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
that enables the AS to inform the client on how to communicate
securely with a RS and that allows the client to indicate
communication security preferences to the AS.
In the OAuth memo defining the key distribution for proof-of-
possession (PoP) tokens [I-D.ietf-oauth-pop-key-distribution], the
authors suggest to use Uri-query parameters in order to submit the
parameters of the client's token request. To avoid large headers if
the client uses CoAP to communicate with the AS, this memo specifies
the following alternative for submitting client request parameters to
the AS: The client encodes the parameters of it's request as a CBOR
map and submits that map as the payload of the client request. The
Content-format MUST be application/cbor in that case.
The OAuth memo further specifies that the AS SHALL use a JSON
structure in the payload of the response 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 the AS SHOULD use
CBOR instead of JSON for encoding it's response. The client can
explicitly request this encoding by using 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
in the communication security protocols it supports. It can
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therefore signal to the AS which protocols it can support for
securing their mutual communication. This is done by using the "csp"
parameter defined below in the Token Request message sent to the AS.
Note that The OAuth key distribution specification
[I-D.ietf-oauth-pop-key-distribution] describes in section 6 how the
client can request specific types of keys (symmetric vs. asymmetric)
and proof-of-possession algorithms in the PoP token request.
The client and the RS might not have any prior knowledge about each
other, therefore the AS needs to help them to establish a security
context or at least a key. The AS does this by indicating
communication security protocol ("csp") and additional key parameters
in the client information.
The "csp" parameter specifies how client and RS communication is
going to be secured based on returned keys. Currently defined values
are "TLS", "DTLS", "ObjectSecurity" with the encodings specified in
Figure 2. Depending on 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 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 from the type of key provided, which (D)TLS
mode the RS supports as follows.
If PreSharedKey mode is used, the AS MUST provide the client with the
pre-shared key to be used with the RS. This key MUST be the same as
the PoP key (i.e. a symmetric key as in section 4 of
[I-D.ietf-oauth-pop-key-distribution]).
The client MUST use the PoP key as DTLS pre-shared key. The client
MUST furthermore use the "kid" parameter provided as part of the JWK/
COSE_Key as the psk_identity in the DTLS handshake [RFC4279].
If RawPublicKey mode is used, the AS MUST provide the client with the
RS's raw public key using the "rpk" parameter defined in the
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following. This parameter MUST contain a JWK or a COSE_Key. The
client MUST provide a raw public key to the AS, and the AS MUST use
this key as PoP key in the token. The token MUST thus use asymmetric
keys for the proof-of-possession.
In order to get the proof-of-possession a RS configured to use this
mode together with PoP tokens MUST require client authentication in
the DTLS handshake. The client MUST use the raw public key bound to
the PoP token for client authentication in DTLS.
TLS or DTLS with certificates MAY make use of pre-established trust
anchors or MAY be configured more tightly with additional client
information parameters, such as x5c, x5t, or x5t#S256. An overview
of these parameters is given below.
For when communication security is based on certificates this
attribute can be used to define the server certificate or CA
certificate. Semantics for this attribute is defined by [RFC7517] or
COSE_Key [I-D.ietf-cose-msg].
For when communication security is based on certificates this
attribute can be used to define the specific server certificate to
expect or the CA certificate. Semantics for this attribute is
defined by JWK/COSE_Key.
To use object security (such as OSCOAP and OSCON) requires security
context to be established, which can be provisioned with PoP token
and client information, or derived from that information. Object
security specifications designed to be used with this protocol MUST
specify the parameters that an AS has to provide to the client in
order to set up the necessary security context.
The RS may support different ways of receiving the access token from
the client (see Section 5.3 and Appendix C). The AS MAY signal the
required method for access token transfer in the client information
by using the "tktr" (token transport) parameter using the 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.
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/-----------+--------------+-------------------------\
| Value | Major Type | Key |
|-----------+--------------+-------------------------|
| 0 | 0 | POST to /authz-info |
| 1 | 0 | RFC 4680 |
| 2 | 0 | CoAP option "Ref-Token" |
\-----------+--------------+-------------------------/
Figure 3: Table of 'tktn' parameter value encodings for Client
Information.
Table Figure 4 summarizes the additional parameters defined here for
use by the client or the AS in the PoP token request protocol.
/-----------+--------------+----------------------------------\
| Parameter | Used by | Description |
|-----------+--------------+----------------------------------|
| csp | client or AS | Communication security protocol |
| rpk | AS | RS's raw public key |
| x5c | AS | RS's X.509 certificate chain |
| x5t | AS | RS's SHA-1 cert thumb print |
| x5t#S256 | AS | RS's SHA-256 cert thumb print |
| tktn | AS | Mode of token transfer C -> RS |
\-----------+--------------+----------------------------------/
Figure 4: Table of additional parameters defined for 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 the option Access-Token. The Access-Token option
is an alternative for transferring the access token when it is
smaller then 255 bytes. If token is larger the 255 bytes lager
authorization information resources MUST at the RS be user when CoAP.
5.3. Authorization Information Resource at the Resource Server
A consequence of allowing the use of CoAP as web transfer protocol is
that we cannot rely on HTTP specific mechanisms, such as transferring
information elements 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 the RS a new resource is
introduced to which the PoP tokens can be sent to convey
authorization information before the first resource request is made
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by the client. This specification calls this resource "/authz-info";
the URI may, however, vary in deployments.
The RS needs to store the PoP token for when later authorizing
requests from the client. The RS is not mandated to be able to
manage multiple client at once. how the RS manages clients is out of
scope for this specification.
5.3.1. Authorization Information Request
The client makes a POST request to the authorization information
resource by sending its PoP token as request data.
Client MUST send the Content-Format option indicate token format
5.3.2. Authorization Information Response
The RS MUST resonde to a requests to 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 requests MUST be answered with 2.01 Created to indicate
that a "session" for the PoP Token has been created. No location
path is required to be returned.
Resource
Client Server
| |
| |
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/authz-info"
| | Content-Format: "application/cwt"
| | Payload: <PoP Token>
| |
B: |<--------+ Header: 2.01 Created
| 2.01 |
| |
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
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is not valid, e.g. wrong audience, the RS MUST return 4.01
Unauthorized.
Resource
Client Server
| |
| |
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path: "/authz-info"
| | Content-Format: "application/cwt"
| | Payload: <PoP Token>
| |
B: |<--------+ Header: 4.01 Unauthorized
| 2.01 |
| |
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. CBOR Data Formats
The /token resource (called "endpoint" in OAuth 2.0), defined in
Section 3.2 of [RFC6749], is used by the client to obtain an access
token. Requests sent to the /token resource use the HTTP POST method
and the payload includes a 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 a received access token. We list
the possibilities here including what functionality they require of
the RS.
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o The token is a CWT/JWT and includes a 'exp' claim and possibly the
'nbf' claim. The RS verifies these by comparing them to values
from its internal clock as defined in [RFC7519]. In this case the
RS must have a real time chip (RTC) or some other way of reliably
measuring time.
o The RS verifies the validity of the token by performing an
introspection request as specified in Appendix D.2. This requires
the RS to have a reliable network connection to the AS and to be
able to handle two secure sessions in parallel (C to RS and AS to
RS).
o The RS and the AS both store a 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 a CWT/JWT. The RS keeps track of the most recently
received sequence number, and only accepts tokens as valid, that
are in a certain range around this number. This method does only
require the RS to keep track of the sequence number. The method
does not provide timely expiration, but it makes sure that older
tokens cease 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 the best that can be
achieved.
6. Deployment Scenarios
There is a large variety 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 to also consider how these requests and
responses between the clients and the resource servers are secured.
The security protocols between other pairs 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 CBOR diagnostic notation for examples of requests
and responses.
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6.1. Client and Resource Server are Offline
In this scenario we consider the case where both the resource server
and the client are offline, i.e., they are not connected to the AS 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 a phase when the client had connectivity to
AS.
Since the resource server must be able to verify the access token
locally, self-contained access tokens must be used.
This example shows the interactions between a client, the
authorization server and a temperature sensor acting as a resource
server. Message exchanges A and B are shown in Figure 7.
A: The client first generates a public-private key pair used for
communication security with the RS.
The client sends the POST request to /token 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: The AS responds with a PoP token and client information. The
PoP token contains the public key of the client, while the client
information contains the public key of the RS. For communication
security this example uses DTLS with raw public keys between the
client and the RS.
Note: In this example we assume that the client knows what
resource it wants to access, and is therefore able to request
specific audience and scope claims for the access token.
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Authorization
Client Server
| |
| |
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"token"
| | Payload: <Request-Payload>
| |
B: |<--------+ Header: 2.05 Content
| | Content-Type: application/cbor
| 2.05 | Payload: <Response-Payload>
| |
Figure 7: Token Request and Response Using Client Credentials.
The information contained in the Request-Payload and the Response-
Payload is shown in Figure 8.
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",
"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" : "P-256",
"x" : b64'MKBCTNIcKUSDii11ySs3526iDZ8AiTo7Tu6KPAqv7D4',
"y" : b64'4Etl6SRW2YiLUrN5vfvVHuhp7x8PxltmWWlbbM4IFyM'
}
Figure 9: Public Key of the RS.
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{
"aud" : "tempSensorInLivingRoom",
"iat" : "1360189224",
"cnf" : {
"jwk" : {
"kid" : b64'1Bg8vub9tLe1gHMzV76e8',
"kty" : "EC",
"crv" : "P-256",
"x" : b64'f83OJ3D2xF1Bg8vub9tLe1gHMzV76e8Tus9uPHvRVEU',
"y" : b64'x_FEzRu9m36HLN_tue659LNpXW6pCyStikYjKIWI5a0'
}
}
}
Figure 10: Access Token including Public Key of the Client.
Messages C and F are shown in Figure 11 - Figure 12.
C: The client then sends the PoP token to the /authz-info resource
at 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 caches the security context together with authorization
information about this client contained in the PoP token.
The client and resource server run 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.
F: The RS responds with a resource representation over DTLS.
Resource
Client Server
| |
C: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"authz-info"
| | Payload: SlAV32hkKG ...
| | (access token)
| |
|<--------+ Header: 2.04 Changed
| 2.04 |
| |
Figure 11: Access Token provisioning to RS
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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 this deployment scenario we consider the case of an RS that may
not be able to access the AS at the time it receives an access
request from a client. We denote this case "RS offline", it involves
steps A, B, C and F of Figure 1.
If the RS 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 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
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 an authorization server. The message exchanges A and B
are shown in Figure 13.
A: The client sends the request POST to /token at AS. The request
contains the Audience parameter set to "tempSensor109797", a value
that the temperature sensor identifies itself with. The scope the
client wants the AS to authorize the access token for is "owner",
which means that the token can be used to both read temperature
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data and upgrade the firmware on the RS. The AS evaluates the
request and authorizes the client 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 RS. The client information contains a symmetric key.
In this case communication security between C and RS is OSCOAP
with an authenticated encryption algorithm. The client derives
two unidirectional security contexts to use with the resource
request 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 to make a GET request
against the /tempC resource and a POST request on the /firmware
resource.
Authorization
Client Server
| |
| |
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path: "token"
| | Payload: <Request-Payload>
| |
B: |<--------+ Header: 2.05 Content
| | Content-Type: application/cbor
| 2.05 | Payload: <Response-Payload>
| |
| |
Figure 13: Token Request and Response
The information contained in the Request-Payload and the Response-
Payload is shown in Figure 14.
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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
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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.
Resource
Client Server
| |
C: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"authz-info"
| | Payload: <Access Token>
| |
| |
|<--------+ Header: 2.04 Changed
| 2.04 |
| |
| |
Figure 16: Access Token provisioning to RS
Resource
Client Server
| |
+-------->| Header: GET (Code=0.01)
| GET | Object-Security:
| | (<seq>,<cid>,[Uri-Path:"tempC"],<tag>)
| |
F: |<--------+ Header: 2.05 Content
| 2.05 | Object-Security:
| | (<seq>,<cid>,[22.7 C],<tag>)
| |
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 of the COSE object: a sequence number
("seq", starting from 0), a context identifier ("cid") indicating the
security context, the ciphertext containing the encrypted CoAP option
identifying the resource, and the Message Authentication Code ("tag")
which also covers the Code in the CoAP header.
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The Object-Security ciphertext in the response [22.7 C] represents an
encrypted temperature reading. (The COSE object is actually carried
in 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
access the AS at the time of the access request. Since the RS is,
however, connected to 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 the client is assumed to be offline, at least for a certain
period 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 is shown in the
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 18.
A: The client sends the request using POST to /token at AS. The
request contains the Audience parameter set to "lockOfDoor4711", a
value the that the online door in question identifies itself with.
The AS generates an access token as on opaque string, which it can
match to the specific client, a targeted audience and a symmetric
key security context.
B: The AS responds with the an access token and client
information, the latter containing a symmetric key. Communication
security between C and RS will be OSCOAP with authenticated
encryption.
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Authorization
Client Server
| |
| |
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"token"
| | Payload: <Request-Payload>
| |
B: |<--------+ Header: 2.05 Content
| | Content-Type: application/cbor
| 2.05 | Payload: <Response-Payload>
| |
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.
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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).
Resource
Client Server
| |
C: +-------->| Header: POST (T=CON, Code=0.02
| POST | Token 0x2a12)
| | Uri-Path:"authz-info"
| | Payload: SlAV32hkKG ...
| | (access token)
| |
|<- - - - + Header: T=ACK
| |
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.
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Resource Authorization
Server Server
| |
D: +--------->| Header: POST (Code=0.02)
| POST | Uri-Path: "introspect"
| | Payload: <Request-Payload>
| |
E: |<---------+ Header: 2.05 Content
| 2.05 | Content-Type: application/cbor)
| | Payload: <Response-Payload>
| |
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.
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Resource
Client Server
| |
+-------->| Header: PUT (Code=0.03)
| PUT | Object-Security:
| | (<seq>,<cid>,[Uri-Path:"lock", 1],<tag>)
| |
F: |<--------+ Header: 2.04 Changed
| 2.04 | Object-Security:
| | (<seq>,<cid>,,<tag>)
| |
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 to the door lock.
In this example there is no ciphertext of the PUT response, but "tag"
contains a MAC which covers the request sequence number and context
identifier as well 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 to receive
commands. As a continuation from the previous scenarios we assume
that both the client and the RS are online at the time of the access
request.
If the client and the resource server are online then the AS should
be configured to issue short-lived access tokens 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 the lack of connectivity constraints there may
still be other restrictions a deployment may face.
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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 access request, as in the "RS offline" case
Section 6.2, it must be offloaded as much message communication as
possible.
OAuth 2.0 is already an efficient protocol in terms of message
exchanges and can be further optimized by compact encodings of
tokens. The scenario illustrated in this section goes beyond that
and removes the access tokens from the protocol. This may be
considered a degenerate case of OAuth 2.0 but it allows us to do two
things:
1. The common case where authorization is performed by means of
authentication fits into the same protocol framework.
Authentication protocol and key is specified 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 is authorized to access
the protected resource.
In case 2., the RS does not need to receive any message from 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, and a MB, not necessarily trusted with access to the plain text
publications. Message exchange A, B is shown in Figure 24.
A: The client sends the request POST to /token at AS. The request
contains the Audience parameter set to "birchPollenSensor301", a
value that characterizes a certain pollen sensor resource. The AS
evaluates the request and authorizes the client to access the
resource.
B: The AS responds with an empty token and client information with
a security context to be used by the client. The empty token
signifies that authorization is performed by means of
authentication using the communication security protocol indicated
with "csp". In this case it is object security of content (OSCON)
i.e. protection of CoAP payload only. The security context
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contains the symmetric decryption key and a public signature
verification key of the RS.
Authorization
Client Server
| |
| |
A: +-------->| Header: POST (Code=0.02)
| POST | Uri-Path:"token"
| | Payload: <Request-Payload>
| |
B: |<--------+ Header: 2.05 Content
| | Content-Type: application/cbor
| 2.05 | Payload: <Response-Payload>
| |
| |
Figure 24: Token Request and Response
The information contained in the Request-Payload and the Response-
Payload 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 RS severely constrained
The content of the "key" parameter is shown in Figure 26.
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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 of the time, occasionally wakes up,
measures the number birch pollens per cubic meters, publishes the
measurements to the MB, and then returns to sleep. See Figure 27.
In this case the birch pollen count stopped at 270, which is
encrypted with the symmetric key and signed with the private key of
the RS. The MB verifies that the message originates from RS using
the public key of RS, that it is not a replay of an old measurement
using the sequence number 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 access token, the client does not address the
/authz-info resource in the RS. The client sends the CoAP request
GET to /birchPollen on MB which is a plain CoAP request.
F: The MB responds with the cached object secured content.
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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 a COSE message consisting of sequence number 'seq'
stepped by the RS for each publication, the context identifier 'cid'
in this case coinciding with the key identifier 'kid' of Figure 26,
the encrypted measurement and the signature by the RS.
Note that the same COSE message format may be used as in OSCOAP but
that only CoAP payload is protected in this case.
The authorization step is implicit, so while any client could request
access the COSE object, only authorized clients have access to the
symmetric key needed to decrypt the content.
Note that in this case the order of the message exchanges A,B and C,F
could in principle be interchanged, i.e. the client could first
request and obtain the protected resource in steps C,F; and after
that request client information containing the keys decrypt and
verify the message.
6.6. Securing Group Communication
There are use cases that require securing communication between a
(group of) senders and a group of receivers. One prominent example
is lighting. Often, a set of lighting nodes (e.g., luminaires, wall-
switches, sensors) are grouped together and only authorized members
of the group must be able read and process messages. Additionally,
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receivers of group messages must be able to verify the integrity of
received messages as being generated within the group.
The requirements for securely communicating in such group use cases
efficiently is outlined in [I-D.somaraju-ace-multicast] along with an
architectural description that aligns with the content of this
document. The requirements for conveying the necessary identifiers
to reference groups and also the process of commissioning devices 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. 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.
8. IANA Considerations
TBD
FIXME: Add registry over 'csp' values from Figure 2
FIXME: Add registry of 'rpk' parameter from section 5.1
FIXME: Add registry of 'tktn' values from Figure 3
8.1. CoAP Option Number Registration
This section registers the "Access-Token" CoAP Option Number
[RFC2046] in "CoRE Parameters" sub-registry "CoAP Option Numbers" in
the manner described in [RFC7252].
Name
Access-Token
Number
TBD
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Reference
[draft-ietf-ace-oauth-authz]
Meaning in Request
Contains an Access Token according to [draft-ietf-ace-oauth-authz]
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 differently. Opaque
data to the client and CWT or reference token to the RS.
Length
Less then 255 bytes
9. 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. References
10.1. Normative References
[I-D.bormann-core-ace-aif]
Bormann, C., "An Authorization Information Format (AIF)
for ACE", draft-bormann-core-ace-aif-03 (work in
progress), July 2015.
[I-D.ietf-cose-msg]
Schaad, J., "CBOR Encoded Message Syntax", draft-ietf-
cose-msg-10 (work in progress), February 2016.
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[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 (work in progress),
March 2015.
[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>.
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[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)",
RFC 7516, DOI 10.17487/RFC7516, May 2015,
<http://www.rfc-editor.org/info/rfc7516>.
[RFC7517] Jones, M., "JSON Web Key (JWK)", RFC 7517,
DOI 10.17487/RFC7517, May 2015,
<http://www.rfc-editor.org/info/rfc7517>.
10.2. 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 (work in
progress), October 2015.
[I-D.ietf-core-block]
Bormann, C. and Z. Shelby, "Block-wise transfers in CoAP",
draft-ietf-core-block-18 (work in progress), September
2015.
[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>.
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[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>.
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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
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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.
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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 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.
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+ 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.
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+ 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
This section sketches some potential optimizations to the presented
solution.
Access token in DTLS handshake
In the case of CSP=DTLS/TLS, the access token provisioning
exchange in step C of 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 the access token.
Reference token and introspection
In case of introspection it may be beneficial to utilize access
tokens which are not self-contained (also known as "reference
tokens") that are used to lookup detailed information about the
authorization. The RS uses the introspection message exchange not
only for validating token claims, but also for obtaining claims
that potentially were not known at the time when the access token
was issued.
A reference token can be made much more compact than a self-
contained token, since it does not need to contain any of claims
that it represents. This could be very useful in particular if
the client is constrained and offline most of the time.
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Reference token in CoAP option
While large access tokens must be sent in CoAP payload, if the
access token is known to be of a certain limited size, for example
in the case of a reference token, then it would be favorable to
combine the access token provisioning request with the resource
request to the RS.
One way to achieve this is to define a new CoAP option for
carrying reference tokens, called "Ref-Token" as shown in the
example in Figure 28.
Resource
Client Server
| |
C: +-------->| Header: PUT (Code=0.02)
| PUT | Ref-Token:SlAV32hkKG
| | Object-Security:
| | <seq>,<cid>,[Uri-Path:"lock", 1],<tag>)
| |
. .
. .
. .
| |
F: |<--------+ Header: 2.04 Changed
| 2.04 | Object-Security:
| | (<seq>,<cid>,,<tag>)
| |
Figure 28: Reference Token in CoAP Option
Appendix D. CoAP 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
is needed. In this appendix we define CoAP resources for the HTTP
based token and introspection endpoints used in vanilla OAuth 2.0.
We also define a CBOR alternative to the JSON and form based POST
structures used in HTTP.
D.1. Profile for Token resource
The token resource is used by the client to obtain an access token by
presenting its authorization grant or client credentials to the
/token resource the AS.
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D.1.1. Token Request
The client makes a request to the token resource by sending a CBOR
structure with the following attributes.
grant_type:
REQUIRED. The grant type, "code", "client_credentials",
"password" or others.
client_id:
OPTIONAL. The client identifier issued to the holder of the token
(client or RS) during the registration process.
client_secret:
OPTIONAL. The client secret.
scope:
OPTIONAL. The scope of the access request as described by
Section 3.1.
aud:
OPTIONAL. Service-specific string identifier or list of string
identifiers representing the intended audience for this token, as
defined in [I-D.wahlstroem-ace-cbor-web-token].
alg:
OPTIONAL. The value in the 'alg' parameter 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 information about the public key
the client would like to bind to the access token in the COSE Key
Structure format.
The parameters defined above use the following CBOR major types.
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/-----------+--------------+-----------------------\
| Value | Major Type | Key |
|-----------+--------------+-----------------------|
| 0 | 0 | grant_type |
| 1 | 0 | client_id |
| 2 | 0 | client_secret |
| 3 | 0 | scope |
| 4 | 0 | aud |
| 5 | 0 | alg |
| 6 | 0 | key |
\-----------+--------------+-----------------------/
Figure 29: CBOR mappings used in token requests
D.1.2. Token Response
The AS responds by sending a CBOR structure with the following
attributes.
access_token:
REQUIRED. The access token issued by the authorization server.
token_type:
REQUIRED. The type of the token issued. "pop" is recommended.
key:
REQUIRED, if symmetric key cryptography is used. A COSE Key
Structure containing the symmetric proof of possession key. The
members of the structure can be found in section 7.1 of
[I-D.ietf-cose-msg].
csp:
REQUIRED. Information on what communication protocol to use in
the communication between the client and the RS. Details on
possible values can be found in Section 5.1.
scope:
OPTIONAL, if identical to the scope requested by the client;
otherwise, REQUIRED.
alg:
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OPTIONAL. The 'alg' parameter provides further information about
the algorithm, such as whether a symmetric or an asymmetric
crypto-system is used.
The parameters defined above use 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 for OAuth Introspection
This section defines a way for a holder of access tokens, mainly
clients and RS's, 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 the token using HTTP POST or HTTP GET. This document reuses
the work done in the OAuth Token Introspection and defines a mapping
of the request and response to CoAP [RFC7252] to be used by
constrained devices.
D.2.1. Introspection Request
The token holder makes a request to the Introspection CoAP resource
by sending 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. The client identifier issued to the holder of the token
(client or RS) during the registration process.
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client_secret:
OPTIONAL. The client secret.
The parameters defined above use the following CBOR major types:
/-----------+--------------+-----------------------\
| Value | Major Type | Key |
|-----------+--------------+-----------------------|
| 0 | 0 | token |
| 1 | 0 | resource_id |
| 2 | 0 | client_id |
| 3 | 0 | client_secret |
\-----------+--------------+-----------------------/
Figure 31: CBOR Mappings to Token Introspection Request Parameters.
D.2.2. Introspection Response
If the introspection request is valid and authorized, the
authorization server returns a CoAP message with the response encoded
as a CBOR structure in the payload of the message. If the request
failed client authentication or is invalid, the authorization server
returns an error response using the CoAP 4.00 'Bad Request' response
code.
The JSON structure in the payload response includes the top-level
members defined in Section 2.2 in the OAuth Token Introspection
specification [I-D.ietf-oauth-introspection]. It is RECOMMENDED to
only return the 'active' attribute considering constrained nature of
CoAP client and server networks.
Introspection responses in CBOR use the following mappings:
active:
REQUIRED. The active key is an indicator of whether or not 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 the information it keeps about its
tokens, but a "true" value return for the "active" property will
generally indicate that 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., after its
issuance time and before its expiration time).
scope:
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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 the client that requested this
token.
username:
OPTIONAL. Human-readable identifier for the resource owner who
authorized this token.
token_type:
OPTIONAL. Type of the token as defined in Section 5.1 of OAuth
2.0 [RFC6749] or PoP token.
exp:
OPTIONAL. Integer timestamp, measured 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].
iat:
OPTIONAL. Integer timestamp, measured 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].
nbf:
OPTIONAL. Integer timestamp, measured 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 the token, as defined in CWT
[I-D.wahlstroem-ace-cbor-web-token]. Usually a machine-readable
identifier of the resource owner who authorized this token.
aud:
OPTIONAL. Service-specific string identifier or list of string
identifiers representing the intended audience for this token, as
defined in CWT [I-D.wahlstroem-ace-cbor-web-token].
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iss:
OPTIONAL. String representing the issuer of this token, as
defined in CWT [I-D.wahlstroem-ace-cbor-web-token].
cti:
OPTIONAL. String identifier for the token, as defined in CWT
[I-D.wahlstroem-ace-cbor-web-token]
The parameters defined above use the following CBOR major types:
/-----------+--------------+-----------------------\
| Value | Major Type | Key |
|-----------+--------------+-----------------------|
| 0 | 0 | active |
| 1 | 0 | scopes |
| 2 | 0 | client_id |
| 3 | 0 | username |
| 4 | 0 | token_type |
| 5 | 0 | exp |
| 6 | 0 | iat |
| 7 | 0 | nbf |
| 8 | 0 | sub |
| 9 | 0 | aud |
| 10 | 0 | iss |
| 11 | 0 | cti |
\-----------+--------------+-----------------------/
Figure 32: CBOR Mappings to Token Introspection Response Parameters.
Appendix E. Document Updates
E.1. 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.
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* 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 the
access token.
o Added 5.2. the CoAP Access-Token option for transfering 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
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Erik Wahlstroem
Nexus Technology
Telefonvagen 26
Hagersten 126 26
Sweden
Email: erik.wahlstrom@nexusgroup.com
Samuel Erdtman
Nexus Technology
Telefonvagen 26
Hagersten 126 26
Sweden
Email: samuel.erdtman@nexusgroup.com
Hannes Tschofenig
ARM Ltd.
Hall in Tirol 6060
Austria
Email: Hannes.Tschofenig@arm.com
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