Alternative Workflow and OAuth Parameters for the Authentication and Authorization for Constrained Environments (ACE) Framework
draft-ietf-ace-workflow-and-params-02
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| Authors | Marco Tiloca , Göran Selander | ||
| Last updated | 2024-07-08 (Latest revision 2024-03-04) | ||
| Replaces | draft-tiloca-ace-workflow-and-params | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-ace-workflow-and-params-02
ACE Working Group M. Tiloca
Internet-Draft RISE AB
Updates: 9200, 9202, 9203, 9431 (if approved) G. Selander
Intended status: Standards Track Ericsson AB
Expires: 9 January 2025 8 July 2024
Alternative Workflow and OAuth Parameters for the Authentication and
Authorization for Constrained Environments (ACE) Framework
draft-ietf-ace-workflow-and-params-02
Abstract
This document updates the Authentication and Authorization for
Constrained Environments Framework (ACE, RFC 9200) as follows.
First, it defines a new, alternative workflow that the Authorization
Server can use for uploading an access token to a Resource Server on
behalf of the Client. Second, it defines new parameters and
encodings for the OAuth 2.0 token endpoint at the Authorization
Server. Third, it defines a method for the ACE framework to enforce
bidirectional access control by means of a single access token.
Fourth, it amends two of the requirements on profiles of the
framework. Finally, it deprecates the original payload format of
error responses that convey an error code, when CBOR is used to
encode message payloads. For such error responses, it defines a new
payload format aligned with RFC 9290, thus updating in this respect
also the profiles of ACE defined in RFC 9202, RFC 9203, and RFC 9431.
About This Document
This note is to be removed before publishing as an RFC.
Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-ace-workflow-and-params/.
Discussion of this document takes place on the Authentication and
Authorization for Constrained Environments (ace) Working Group
mailing list (mailto:ace@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/ace/. Subscribe at
https://www.ietf.org/mailman/listinfo/ace/.
Source for this draft and an issue tracker can be found at
https://github.com/ace-wg/ace-workflow-and-params.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright (c) 2024 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 (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. New ACE Workflow . . . . . . . . . . . . . . . . . . . . . . 6
3. New ACE Parameters . . . . . . . . . . . . . . . . . . . . . 10
3.1. token_upload . . . . . . . . . . . . . . . . . . . . . . 10
3.1.1. Examples . . . . . . . . . . . . . . . . . . . . . . 11
3.2. token_hash . . . . . . . . . . . . . . . . . . . . . . . 16
3.2.1. Computing the Token Hash . . . . . . . . . . . . . . 17
3.2.2. Example . . . . . . . . . . . . . . . . . . . . . . . 18
3.3. rs_cnf2 and aud2 . . . . . . . . . . . . . . . . . . . . 20
3.3.1. Example . . . . . . . . . . . . . . . . . . . . . . . 21
3.4. anchor_cnf . . . . . . . . . . . . . . . . . . . . . . . 22
3.4.1. Example . . . . . . . . . . . . . . . . . . . . . . . 24
3.5. rev_aud . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.6. rev_scope . . . . . . . . . . . . . . . . . . . . . . . . 26
4. Bidirectional Access Control . . . . . . . . . . . . . . . . 27
4.1. Scenario with One Authorization Server . . . . . . . . . 28
4.1.1. Access Token Request . . . . . . . . . . . . . . . . 28
4.1.2. Access Token Response . . . . . . . . . . . . . . . . 29
4.1.3. Access to Protected Resources . . . . . . . . . . . . 32
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4.2. Scenario with Two Authorization Servers . . . . . . . . . 32
4.3. Practical Considerations . . . . . . . . . . . . . . . . 32
5. Updated Requirements on Profiles . . . . . . . . . . . . . . 33
6. Updated Payload Format of Error Responses . . . . . . . . . . 33
7. Security Considerations . . . . . . . . . . . . . . . . . . . 36
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
8.1. OAuth Parameters Registry . . . . . . . . . . . . . . . . 36
8.2. OAuth Parameters CBOR Mappings Registry . . . . . . . . . 38
8.3. JSON Web Token Claims Registry . . . . . . . . . . . . . 39
8.4. CBOR Web Token (CWT) Claims Registry . . . . . . . . . . 40
8.5. Custom Problem Detail Keys Registry . . . . . . . . . . . 40
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 41
9.1. Normative References . . . . . . . . . . . . . . . . . . 41
9.2. Informative References . . . . . . . . . . . . . . . . . 44
Appendix A. Benefits for ACE Transport Profiles . . . . . . . . 44
A.1. DTLS Profile . . . . . . . . . . . . . . . . . . . . . . 45
A.2. EDHOC and OSCORE Profile . . . . . . . . . . . . . . . . 45
Appendix B. Open Points . . . . . . . . . . . . . . . . . . . . 46
B.1. New Workflow . . . . . . . . . . . . . . . . . . . . . . 46
B.1.1. Allow the Dynamic Update of Access Rights . . . . . . 46
B.1.2. Ensure Applicability to Any ACE Profile . . . . . . . 48
B.2. Further New Parameters to Consider . . . . . . . . . . . 48
Appendix C. CDDL Model . . . . . . . . . . . . . . . . . . . . . 50
Appendix D. Document Updates . . . . . . . . . . . . . . . . . . 50
D.1. Version -01 to -02 . . . . . . . . . . . . . . . . . . . 50
D.2. Version -00 to -01 . . . . . . . . . . . . . . . . . . . 51
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51
1. Introduction
The Authentication and Authorization for Constrained Environments
(ACE) framework [RFC9200] defines an architecture to enforce access
control for constrained devices. A Client (C) requests an assertion
of granted permissions from an Authorization Server (AS) in the form
of an access token, then uploads the access token to the target
Resource Server (RS), and finally accesses protected resources at the
RS according to the permissions specified in the access token.
The framework has as main building blocks the OAuth 2.0 framework
[RFC6749], the Constrained Application Protocol (CoAP) [RFC7252] for
message transfer, CBOR [RFC8949] for compact encoding, and COSE
[RFC9052][RFC9053] for self-contained protection of access tokens.
In addition, separate profile documents define in detail how the
participants in the ACE architecture communicate, especially as to
the security protocols that they use.
This document updates [RFC9200] as follows.
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* It defines a new, alternative protocol workflow for the ACE
framework (see Section 2), according to which the AS uploads the
access token to the RS on behalf of C, and then informs C about
the outcome. The new workflow is especially convenient in
deployments where the communication leg between C and the RS is
constrained, but the communication leg between the AS and the RS
is not.
The new workflow has no ambition to replace the original workflow.
The AS can use one workflow or the other depending, for example,
on the specific RS for which an access token has been issued and
the nature of the communication leg with that RS.
* It defines additional parameters and encodings for the OAuth 2.0
token endpoint at the AS (see Section 3). These include:
- "token_upload", used by C to inform the AS that it opts in to
use the new ACE workflow, and by the AS to inform C about the
outcome of the token uploading to the RS per the new workflow.
- "token_hash", used by the AS to provide C with a token hash,
corresponding to an access token that the AS has issued for C
and has successfully uploaded to the RS on behalf of C per the
new ACE workflow.
- "rs_cnf2", used by the AS to provide C with the public keys of
the RSs in the group-audience for which the access token is
issued (see Section 6.9 of [RFC9200]).
- "aud2", used by the AS to provide C with the identifiers of the
RSs in the group-audience for which the access token is issued.
- "anchor_cnf", used by the AS to provide C with the public keys
of trust anchors, which C can use to validate the public key of
an RS (e.g., as provided in the "rs_cnf" parameter defined in
[RFC9201] or in the "rs_cnf2" parameter defined in this
document).
- "rev_aud", used by C to provide the AS with an identifier of
itself as a reverse audience, and by the AS to possibly confirm
that identifier in a response to C. A corresponding access
token claim, namely "rev_aud", is also defined.
- "rev_scope", used by C to ask the AS that the requested access
token specifies additional access rights as a reverse scope,
allowing the access token's audience to accordingly access
protected resources at C. This parameter is also used by the
AS to provide C with the access rights that are actually
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granted as reverse scope to the access token's audience. A
corresponding access token claim, namely "rev_scope", is also
defined.
* It defines a method for the ACE framework to enforce bidirectional
access control by means of a single access token (see Section 4),
building on the two new parameters "rev_aud" and "rev_scope" as
well as on the corresponding access token claims.
* It amends two of the requirements on profiles of the ACE framework
(see Section 5).
* It deprecates the original payload format of error responses that
convey an error code, when CBOR is used to encode message payloads
in the ACE framework. For such error responses, it defines a new
payload format according to the problem-details format specified
in [RFC9290] (see Section 6).
In this respect, it also updates the profiles of the ACE framework
defined in [RFC9202], [RFC9203], and [RFC9431].
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Readers are expected to be familiar with the terms and concepts
described in the ACE framework for Authentication and Authorization
[RFC9200][RFC9201], as well as with terms and concepts related to
CBOR Web Tokens (CWTs) [RFC8392] and CWT Confirmation Methods
[RFC8747].
The terminology for entities in the considered architecture is
defined in OAuth 2.0 [RFC6749]. In particular, this includes Client
(C), Resource Server (RS), and Authorization Server (AS).
Readers are also expected to be familiar with the terms and concepts
related to CoAP [RFC7252], CDDL [RFC8610], CBOR [RFC8949], JSON
[RFC8259], and COSE [RFC9052][RFC9053].
Note that the term "endpoint" is used here following its OAuth
definition [RFC6749], aimed at denoting resources such as /token and
/introspect at the AS, and /authz-info at the RS. This document does
not use the CoAP definition of "endpoint", which is "An entity
participating in the CoAP protocol."
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Furthermore, this document uses the following term.
* Token series: the set comprising all the access tokens issued by
the same AS for the same pair (Client, Resource Server).
Profiles of ACE can provide their extended and specialized
definition, e.g., by further taking into account the public
authentication credentials of C and the RS.
* Token hash: identifier of an access token, in binary format
encoding. The token hash has no relation to other possibly used
token identifiers, such as the 'cti' (CWT ID) claim of CBOR Web
Tokens (CWTs) [RFC8392].
Concise Binary Object Representation (CBOR) [RFC8949] and Concise
Data Definition Language (CDDL) [RFC8610] are used in this document.
CDDL predefined type names, especially bstr for CBOR byte strings and
tstr for CBOR text strings, are used extensively in this document.
Examples throughout this document are expressed in CBOR diagnostic
notation as defined in Section 8 of [RFC8949] and Appendix G of
[RFC8610]. Diagnostic notation comments are often used to provide a
textual representation of the numeric parameter names and values.
In the CBOR diagnostic notation used in this document, constructs of
the form e'SOME_NAME' are replaced by the value assigned to SOME_NAME
in the CDDL model shown in Figure 11 of Appendix C. For example,
{e'aud_2' : ["rs1", "rs2"]} stands for {49 : ["rs1", "rs2"]}.
Note to RFC Editor: Please delete the paragraph immediately preceding
this note. Also, in the CBOR diagnostic notation used in this
document, please replace the constructs of the form e'SOME_NAME' with
the value assigned to SOME_NAME in the CDDL model shown in Figure 11
of Appendix C. Finally, please delete this note.
2. New ACE Workflow
As defined in Section 4 of [RFC9200], the ACE framework considers
what is shown in Figure 1 as its basic protocol workflow.
That is, the Client first sends an Access Token Request to the token
endpoint at the AS (step A), specifying permissions that it seeks to
obtain for accessing protected resources at the RS, possibly together
with information on its own public authentication credentials.
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Then, if the request has been successfully verified, authenticated,
and authorized, the AS replies to the Client (step B), providing an
access token and possibly additional parameters as access information
including the actually granted permissions.
Finally, the Client uploads the access token to the RS and,
consistently with the permissions granted according to the access
token, accesses a resource at the RS (step C), which replies with the
result of the resource access (step F). Details about what protocol
the Client and the RS use to establish a secure association, mutually
authenticate, and secure their communications are defined in the
specifically used profile of ACE, e.g., [RFC9202][RFC9203][RFC9431][I
-D.ietf-ace-edhoc-oscore-profile][I-D.ietf-ace-group-oscore-profile][
RFC9431].
Further interactions are possible between the AS and the RS, i.e.,
the exchange of an introspection request and response where the AS
validates a previously issued access token for the RS (steps D and
E).
+--------+ +---------------+
| |---(A)-- Token Request ------->| |
| | | Authorization |
| |<--(B)-- Access Token ---------| Server |
| | + Access Information | |
| | + Refresh Token (optional) +---------------+
| | ^ |
| | Introspection Request (D)| |
| Client | Response | |(E)
| | (optional exchange) | |
| | | v
| | +--------------+
| |---(C)-- Token + Request ----->| |
| | | Resource |
| |<--(F)-- Protected Resource ---| Server |
| | | |
+--------+ +--------------+
Figure 1: ACE Basic Protocol Workflow.
This section defines a new, alternative protocol workflow shown in
Figure 2, which MAY be supported by the AS. Unlike in the original
protocol workflow, the AS uploads the access token to the RS on
behalf of the Client, and then informs the Client about the outcome.
If the token uploading has been successfully completed, the AS does
not provide the access token to the Client altogether. Instead, the
Client simply establishes a secure association with the RS (if that
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has not happened already), and then accesses protected resources at
the RS according to the permissions granted per the access token and
specified by the AS as access information.
+--------+ +----------------------------+
| |---(A)-- Token Request ------->| |
| | | Authorization |
| |<--(B)-- Token Response -------| Server |
| | + Access Information | |
| | + Access Token (optional) +----------------------------+
| | + Refresh Token (optional) ^ | | ^
| | | | | | Token-Upload
| | Introspection Request (D)| | (A1)| | Request
| Client | Response | |(E) | |(A2) Response
| | (optional exchange) | | | |
| | | v v |
| | +----------------------------+
| |---(C1)-- Token (Optional) --->| |
| | | |
| |---(C2)-- Protected Request -->| Resource |
| | | Server |
| |<--(F)--- Protected Resource --| |
| | | |
+--------+ +----------------------------+
Figure 2: ACE Alternative Protocol Workflow.
More specifically, the new workflow consists of the following steps.
* Step A - Like in the original workflow, the Client sends an Access
Token Request to the token endpoint at the AS, with the additional
indication that it opts in to use the alternative workflow.
As defined in Section 3.1, this information is conveyed to the AS
by means of the "token_upload" parameter. The parameter also
specifies what the AS has to return in the Token Response at step
B, following a successful uploading of the access token from the
AS to the RS.
* Step A1 - This new step consists of the AS uploading the access
token to the RS, typically at the authz-info endpoint, just like
the Client does in the original workflow.
* Step A2 - This new step consists of the RS replying to the AS,
following the uploading of the access token at step A1.
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* Step B - In the Access Token Response, the AS tells the Client
that it has attempted to upload the access token to the RS,
specifying the outcome of the token uploading based on the reply
received from the RS at step A2.
As defined in Section 3.1, this information is conveyed to the
Client by means of the "token_upload" parameter included in the
Access Token Response. If the token uploading has failed, the
Access Token Response also includes the access token. Otherwise,
the Access Token Response includes information consistent with
what was specified by the "token_upload" parameter of the Access
Token Request at Step A.
* Step C1 - This step occurs only if the token uploading from the AS
has failed, and the AS has provided the Client with the access
token at step B. In such a case, the Client uploads the access
token to the RS just like at step C of the original workflow.
* Step C2 - The Client attempts to access a protected resource at
the RS, according to the permissions granted per the access token
and specified by the AS as access information at step B.
* Steps D, E, and F are as in the original workflow.
The new workflow has no ambition to replace the original workflow
defined in [RFC9200]. The AS can use one workflow or the other
depending, for example, on the specific RS for which the access token
has been issued and the nature of the communication leg with that RS.
When using the new workflow, all the communications between the AS
and the RS MUST be protected, consistent with Sections 5.8.4.3 and
6.5 of [RFC9200]. Unlike in the original workflow, this results in
protecting also the uploading of the first access token in a token
series, i.e., in addition to the uploading of the following access
tokens in the token series for dynamically updating the access rights
of the Client.
Note that the new workflow is also suitable for deployments where
devices meant to access protected resources at the RS are not
required to be actual ACE Clients. That is, consistent with intended
access policies, the AS can be configured to automatically issue
access tokens for such devices and upload those access tokens to the
RS. This means that those devices do not have to request for an
access token to be issued in the first place, and instead can
immediately send requests to the RS for accessing its protected
resources, in accordance to the access tokens already issued and
uploaded by the AS.
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3. New ACE Parameters
The rest of this section defines a number of additional parameters
and encodings for the OAuth 2.0 token endpoint at the AS.
3.1. token_upload
This section defines the additional "token_upload" parameter. The
parameter can be used in an Access Token Request sent by C to the
token endpoint at the AS, as well as in the successful Access Token
Response sent as reply by the AS.
* The "token_upload" parameter is OPTIONAL in an Access Token
Request. The presence of this parameter indicates that C opts in
to use the new, alternative ACE workflow defined in Section 2,
whose actual use for uploading the issued access token to the RS
is an exclusive prerogative of the AS.
This parameter can take one of the following integer values. When
the Access Token Request is encoded in CBOR, those values are
encoded as CBOR unsigned integers. The value of the parameter
determines whether the follow-up successful Access Token Response
will have to include certain information, in case the AS has
successfully uploaded the access token to the RS.
- 0: The Access Token Response will have to include neither the
access token nor its corresponding token hash.
- 1: The Access Token Response will have to include the token
hash corresponding to the access token, but not the access
token.
- 2: The Access Token Response will have to include the access
token, but not the corresponding token hash.
If the AS supports the new ACE workflow and the Access Token
Request includes the "token_upload" parameter with value 0, 1, or
2, then the AS MAY use the new ACE workflow to upload the access
token to the RS on behalf of C. Otherwise, the AS MUST NOT use
the new ACE workflow.
* The "token_upload" parameter is REQUIRED in a successful Access
Token Response with response code 2.01 (Created), if both the
following conditions apply. Otherwise, the "token_upload"
parameter MUST NOT be present.
- The corresponding Access Token Request included the
"token_upload" parameter, with value 0, 1, or 2.
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- The AS has attempted to upload the issued access token to the
RS as per the new ACE workflow, irrespective of the result of
the token upload.
When the "token_upload" parameter is present in the Access Token
Response, it can take one of the following integer values. When
the Access Token Response is encoded in CBOR, those values are
encoded as CBOR unsigned integers.
- If the token upload to the RS was not successful, then the
"token_upload" parameter MUST specify the value 1.
In this case, the Access Token Response MUST include the
"access_token" parameter specifying the issued access token.
- If the token upload at the RS was successful, then the
"token_upload" parameter MUST specify the value 0.
In this case, the Access Token Response can include additional
parameters as defined below, depending on the value of the
"token_upload" parameter in the corresponding Access Token
Request.
o If the "token_upload" parameter in the Access Token Request
specified the value 0, then the Access Token Response MUST
NOT include the "access_token" parameter and MUST NOT
include the "token_hash" parameter defined in Section 3.2.
o If the "token_upload" parameter in the Access Token Request
specified the value 1, then the Access Token Response MUST
NOT include the "access_token" parameter and MUST include
the "token_hash" parameter defined in Section 3.2,
specifying the hash corresponding to the issued access token
and computed as defined in Section 3.2.
o If the "token_upload" parameter in the Access Token Request
specified the value 2, then the Access Token Response MUST
include the "access_token" parameter specifying the issued
access token and MUST NOT include the "token_hash" parameter
defined in Section 3.2.
3.1.1. Examples
Figure 3 shows an example with first an Access Token Request from C
to the AS, and then an Access Token Response from the AS to C,
following the issue of an access token bound to a symmetric PoP key.
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The Access Token Request specifies the "token_upload" parameter with
value 0. That is, C indicates that it requires neither the access
token nor the corresponding token hash from the AS, in case the AS
successfully uploads the access token to the RS.
The Access Token Response specifies the "token_upload" parameter with
value 0, which indicates that the AS has successfully uploaded the
access token to the RS on behalf of C.
Consistent with the value of the "token_upload" parameter in the
Access Token Request, the Access Token Response includes neither the
access token nor its corresponding token hash. The Access Token
Response also includes the "cnf" parameter specifying the symmetric
PoP key bound to the access token.
/ Access Token Request /
Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: application/ace+cbor
Payload:
{
/ audience / 5 : "tempSensor4711",
/ scope / 9 : "read",
e'token_upload' : 0
}
/ Access Token Response /
Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Max-Age: 3560
Payload:
{
e'token_upload' : 0,
/ expires_in / 2 : 3600,
/ cnf / 8 : {
/ COSE_Key / 1 : {
/ kty / 1 : 4 / Symmetric /,
/ kid / 2 : h'3d027833fc6267ce',
/ k / -1 : h'73657373696f6e6b6579'
}
}
}
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Figure 3: Example of Access Token Request-Response Exchange.
Following a successful uploading of the access token from the AS
to the RS, the Access Token Response includes the "token_upload"
parameter but not the access token, which is bound to a symmetric
key and was uploaded to the RS by the AS.
Figure 4 shows another example with first an Access Token Request
from C to the AS, and then an Access Token Response from the AS to C,
following the issue of an access token bound to a symmetric PoP key.
The Access Token Request specifies the "token_upload" parameter with
value 2. That is, C indicates that it requires the access token from
the AS, even in case the AS successfully uploads the access token to
the RS.
The Access Token Response specifies the "token_upload" parameter with
value 0, which indicates that the AS has successfully uploaded the
access token to the RS on behalf of C.
Consistent with the value of the "token_upload" parameter in the
Access Token Request, the Access Token Response includes the
"access_token" parameter specifying the issued access token. The
Access Token Response also includes the "cnf" parameter specifying
the symmetric PoP key bound to the access token.
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/ Access Token Request /
Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: application/ace+cbor
Payload:
{
/ audience / 5 : "tempSensor4711",
/ scope / 9 : "read",
e'token_upload' : 2
}
/ Access Token Response /
Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Max-Age: 3560
Payload:
{
e'token_upload' : 0,
/ access_token / 1 : h'd08343a1'/...
(remainder of CWT omitted for brevity;
CWT contains the symmetric PoP key in the "cnf" claim)/,
/ expires_in / 2 : 3600,
/ cnf / 8 : {
/ COSE_Key / 1 : {
/ kty / 1 : 4 / Symmetric /,
/ kid / 2 : h'3d027833fc6267ce',
/ k / -1 : h'73657373696f6e6b6579'
}
}
}
Figure 4: Example of Access Token Request-Response Exchange.
Following a successful uploading of the access token from the AS
to the RS, the Access Token Response includes the "token_upload"
parameter as well as the "access_token" parameter conveying the
access token, which is bound to a symmetric key and was uploaded
to the RS by the AS.
Figure 5 shows another example with first an Access Token Request
from C to the AS, and then an Access Token Response from the AS to C,
also following the issue of an access token bound to a symmetric PoP
key.
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The Access Token Request specifies the "token_upload" parameter with
value 0. That is, C indicates that it requires neither the access
token nor the corresponding token hash from the AS, in case the AS
successfully uploads the access token to the RS.
In this example, the Access Token Response includes the
"token_upload" parameter with value 1, which indicates that the AS
has attempted and failed to upload the access token to the RS on
behalf of C. The Access Token Response also includes the
"access_token" parameter specifying the issued access token, together
with the "cnf" parameter specifying the symmetric PoP key bound to
the access token.
Note that, even though the AS has failed to upload the access token
to the RS, the response code 2.01 (Created) is used when replying to
C, since the Access Token Request as such has been successfully
processed at the AS, with the following issue of the access token.
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/ Access Token Request /
Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: application/ace+cbor
Payload:
{
/ audience / 5 : "tempSensor4711",
/ scope / 9 : "read",
e'token_upload' : 0
}
/ Access Token Response /
Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Max-Age: 3560
Payload:
{
e'token_upload' : 1,
/ access_token / 1 : h'd08343a1'/...
(remainder of CWT omitted for brevity;
CWT contains the symmetric PoP key in the "cnf" claim)/,
/ expires_in / 2 : 3600,
/ cnf / 8 : {
/ COSE_Key / 1 : {
/ kty / 1 : 4 / Symmetric /,
/ kid / 2 : h'3d027833fc6267ce',
/ k / -1 : h'73657373696f6e6b6579'
}
}
}
Figure 5: Example of Access Token Request-Response Exchange.
Following a failed uploading of the access token from the AS to
the RS, the Access Token Response includes the "token_upload"
parameter with value 1 as well the "access_token" parameter
conveying the access token bound to a symmetric key.
3.2. token_hash
This section defines the additional "token_hash" parameter. The
parameter can be used in a successful Access Token Response sent as
reply by the AS to C.
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The following refers to the base64url encoding without padding (see
Section 5 of [RFC4648]), and denotes as "binary representation" of a
text string the corresponding UTF-8 encoding [RFC3629], which is the
implied charset used in JSON (see Section 8.1 of [RFC8259]).
The "token_hash" parameter is REQUIRED in a successful Access Token
Response with response code 2.01 (Created), if both the following
conditions apply. Otherwise, the "token_hash" parameter MUST NOT be
present.
* The corresponding Access Token Request included the "token_upload"
parameter with value 1.
* The Access Token Response includes the "token_upload" parameter
with value 0. That is, the AS has successfully uploaded the
issued access token to the RS, as per the new ACE workflow.
This parameter specifies the token hash corresponding to the access
token issued by the AS and successfully uploaded to the RS on behalf
of C. In particular:
* If the Access Token Response is encoded in CBOR, then the
"token_hash" parameter is a CBOR byte string, with value the token
hash.
* If the Access Token Response is encoded in JSON, then the
"token_hash" parameter has as value the binary representation of
the base64url-encoded text string that encodes the token hash.
The AS computes the token hash as defined in Section 3.2.1.
3.2.1. Computing the Token Hash
The AS computes the token hash over the value that the "access_token"
parameter would have had in the same Access Token Response, if it was
included therein and specifying the access token.
In particular, the input HASH_INPUT over which the token hash is
computed is determined as follows.
* If the Access Token Response is encoded in CBOR, then:
- BYTES denotes the value of the CBOR byte string that would be
conveyed by the "access_token" parameter, if this was included
in the Access Token Response.
- HASH_INPUT_TEXT is the base64url-encoded text string that
encodes BYTES.
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- HASH_INPUT is the binary representation of HASH_INPUT_TEXT.
* If the Access Token Response is encoded in JSON, then HASH_INPUT
is the binary representation of the text string conveyed by the
"access_token" parameter, if this was included in the Access Token
Response.
Once determined HASH_INPUT as defined above, a hash value of
HASH_INPUT is generated as per Section 6 of [RFC6920]. The resulting
output in binary format is used as the token hash. Note that the
used binary format embeds the identifier of the used hash function,
in the first byte of the computed token hash.
The specifically used hash function MUST be collision-resistant on
byte-strings, and MUST be selected from the "Named Information Hash
Algorithm" Registry [Named.Information.Hash.Algorithm].
The computation of token hashes defined above is aligned with that
specified for the computation of token hashes in
[I-D.ietf-ace-revoked-token-notification], where they are used as
identifiers of revoked access tokens. Therefore, given a hash
algorithm and an access token, the AS computes the same corresponding
token hash in either case.
If the AS supports the method specified in
[I-D.ietf-ace-revoked-token-notification], then the AS MUST use the
same hash algorithm for computing both the token hashes to include in
the "token_hash" parameter and the token hashes computed per such a
method to identify revoked access tokens.
3.2.2. Example
Figure 6 shows an example with first an Access Token Request from C
to the AS, and then an Access Token Response from the AS to C,
following the issue of an access token bound to a symmetric PoP key.
The Access Token Request specifies the "token_upload" parameter with
value 1. That is, C indicates that it requires the token hash
corresponding to the access token from the AS, in case the AS
successfully uploads the access token to the RS.
The Access Token Response specifies the "token_upload" parameter with
value 0, which indicates that the AS has successfully uploaded the
access token to the RS on behalf of C.
Consistent with the value of the "token_upload" parameter in the
Access Token Request, the Access Token Response includes the
"token_hash" parameter, which specifies the token hash corresponding
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to the issued access token. The Access Token Response also includes
the "cnf" parameter specifying the symmetric PoP key bound to the
access token.
/ Access Token Request /
Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: application/ace+cbor
Payload:
{
/ audience / 5 : "tempSensor4711",
/ scope / 9 : "read",
e'token_upload' : 1
}
/ Access Token Response /
Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Max-Age: 3560
Payload:
{
e'token_upload' : 0,
e'token_hash' : h'0153269057e12fe2b74ba07c892560a2d7
53877eb62ff44d5a19002530ed97ffe4',
/ expires_in / 2 : 3600,
/ cnf / 8 : {
/ COSE_Key / 1 : {
/ kty / 1 : 4 / Symmetric /,
/ kid / 2 : h'3d027833fc6267ce',
/ k / -1 : h'73657373696f6e6b6579'
}
}
}
Figure 6: Example of Access Token Request-Response Exchange.
Following a successful uploading of the access token from the AS
to the RS, the Access Token Response includes the "token_upload"
parameter as well as the "token_hash" parameter. The
"token_hash" parameter conveys the token hash corresponding to
the issued access token, which is bound to a symmetric key and
was uploaded to the RS by the AS.
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3.3. rs_cnf2 and aud2
This section defines the additional parameters "rs_cnf2" and "aud2"
for an Access Token Response, sent by the AS in reply to a request to
the token endpoint from C.
* The "rs_cnf2" parameter is OPTIONAL if the token type is "pop",
asymmetric keys are used, and the access token is issued for an
audience that includes multiple RSs (i.e., a group-audience, see
Section 6.9 of [RFC9200]). Otherwise, the "rs_cnf2" parameter
MUST NOT be present.
This parameter specifies information about the public keys used by
the RSs of a group-audience for authenticating themselves to C,
and is used in case the binding between the public keys and the
corresponding RS identities are not established through other
means. If this parameter is absent, either the RSs in the group-
audience do not use a public key, or the AS knows that the RSs can
authenticate themselves to C without additional information.
If present, this parameter MUST encode a non-empty CBOR array of N
elements, where N is the number of RSs in the group-audience for
which the access token is issued. Each element of the CBOR array
specifies the public key of one RS in the group-audience, and MUST
follow the syntax and semantics of the "cnf" claim either from
Section 3.1 of [RFC8747] for CBOR-based interactions, or from
Section 3.1 of [RFC7800] for JSON-based interactions. It is not
required that all the elements of the CBOR array rely on the same
confirmation method.
Each of the public keys may contain parameters specifying
information such as the public key algorithm and use (e.g., by
means of the parameters "alg" or "key_ops" in a COSE_Key
structure). If such information is specified, a Client MUST NOT
use a public key that is incompatible with the profile or PoP
algorithm according to that information. An RS MUST reject a
proof of possession using such a key with a response code
equivalent to the CoAP code 4.00 (Bad Request).
* The "aud2" parameter is OPTIONAL and specifies the identifiers of
the RSs in the group-audience for which the access token is
issued.
If present, this parameter MUST encode a non-empty CBOR array of N
elements, where N is the number of RSs in the group-audience for
which the access token is issued. Each element of the CBOR array
in the "aud2" parameter MUST be a CBOR text string, with value the
identifier of one RS in the group-audience.
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The element of the CBOR array referring to an RS in the group-
audience SHOULD have the same value that would be used to identify
that RS through the "aud" parameter of an Access Token Request to
the AS (see Section 5.8.2 of [RFC9200]) and of an Access Token
Response from the AS (see Section 5.8.2 of [RFC9200]), when
requesting and issuing an access token for that individual RS.
The "aud2" parameter is REQUIRED if the "rs_cnf2" parameter is
present. In such a case, the i-th element of the CBOR array in
the "aud2" parameter MUST be the identifier of the RS whose public
key is specified as the i-th element of the CBOR array in the
"rs_cnf2" parameter.
3.3.1. Example
Figure 7 shows an example of Access Token Response from the AS to C,
following the issue of an access token for a group-audience composed
of two RSs "rs1" and "rs2", and bound to C's public key as asymmetric
PoP key. The Access Token Response includes the access token, as
well as the parameters "aud2" and "rs_cnf2". These specify the
public key of the two RSs as intended recipients of the access token
and the identifiers of those two RSs, respectively.
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Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Max-Age: 3600
Payload:
{
/ access_token / 1 : b64'SlAV32hk'/...
(remainder of CWT omitted for brevity;
CWT contains the client's RPK in the "cnf" claim)/,
/ expires_in / 2 : 3600,
e'aud2' : ["rs1", "rs2"],
e'rs_cnf2' : [
{
/ COSE_Key / 1 : {
/ kty / 1 : 2 / EC2 /,
/ crv / -1 : 1 / P-256 /,
/ x / -2 : h'bbc34960526ea4d32e940cad2a234148
ddc21791a12afbcbac93622046dd44f0',
/ y / -3 : h'4519e257236b2a0ce2023f0931f1f386
ca7afda64fcde0108c224c51eabf6072'
}
},
{
/ COSE_Key / 1 : {
/ kty / 1 : 2 / EC2 /,
/ crv / -1 : 1 / P-256 /,
/ x / -2 : h'ac75e9ece3e50bfc8ed6039988952240
5c47bf16df96660a41298cb4307f7eb6',
/ y / -3 : h'6e5de611388a4b8a8211334ac7d37ecb
52a387d257e6db3c2a93df21ff3affc8'
}
}
]
}
Figure 7: Example of Access Token Response with an access token
bound to an asymmetric key, using the parameters "aud2" and
"rs_cnf2".
3.4. anchor_cnf
This section defines the additional "anchor_cnf" parameter for an
Access Token Response, sent by the AS in reply to a request to the
token endpoint from C.
The "anchor_cnf" parameter is OPTIONAL if the token type is "pop" and
asymmetric keys are used. Otherwise, the "anchor_cnf" parameter MUST
NOT be present.
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This parameter specifies information about the public keys of trust
anchors, which C can use to validate the public key of the RS/RSs
included in the audience for which the access token is issued. This
parameter can be used when the access token is issued for an audience
including one RS or multiple RSs.
If this parameter is absent, either the RS/RSs in the audience do not
use a public key, or the AS knows that C can validate the public key
of such RS/RSs without additional information (e.g., C has already
obtained the required public keys of the involved trust anchors from
the AS or through other means).
If present, this parameter MUST encode a non-empty CBOR array that
MUST be treated as a set, i.e., the order of its elements has no
meaning. Each element of the CBOR array specifies the public key of
one trust anchor, which can be used to validate the public key of at
least one RS included in the audience for which the access token is
issued. Each element of the CBOR array MUST follow the syntax and
semantics of the "cnf" claim either from Section 3.1 of [RFC8747] for
CBOR-based interactions, or from Section 3.1 of [RFC7800] for JSON-
based interactions. It is not required that all the elements of the
CBOR array rely on the same confirmation method.
Each of the public keys specified in the "anchor_cnf" parameter may
contain parameters specifying information such as the public key
algorithm and use (e.g., by means of the parameters "alg" or
"key_ops" in a COSE_Key structure). If such information is
specified, a Client MUST NOT use a public key that is incompatible
with the profile, or with the public keys to validate and the way to
validate those.
The presence of this parameter does not require that the Access Token
Response also includes the "rs_cnf" parameter defined in [RFC9201] or
the "rs_cnf2" parameter defined in Section 3.3 of this document.
That is, C may be able to obtain the public keys of the RS/RSs for
which the access token is issued through other means.
When the Access Token Response includes both the "anchor_cnf"
parameter and the "aud2" parameter defined in Section 3.3, then C
MUST make sure that a public key PK_RS is associated with an RS
identified by an element of "aud2", before using any of the public
keys specified in "anchor_cnf" to validate PK_RS.
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When the Access Token Response includes the "anchor_cnf" parameter
but not the "aud2" parameter, then C can use any of the public keys
specified in "anchor_cnf" to validate the public key PK_RS of any RS
in the targeted audience. This allows C to use the access token with
an RS that is deployed later on as part of the same audience, which
is particularly useful in the case of a group-audience.
3.4.1. Example
Figure 8 shows an example of Access Token Response from the AS to C,
following the issue of an access token for a group-audience, and
bound to C's public key as asymmetric PoP key.
The identifier of the group-audience was specified by the "aud"
parameter of the Access Token Request to the AS and is specified by
the "aud" claim of the issued access token, and is not repeated in
the Access Token Response from the AS.
The Access Token Response includes the "anchor_cnf" parameter. This
specifies the public key of a trust anchor that C can use to validate
the public keys of any RS with which the access token is going to be
used. The public key of the trust anchor is here conveyed within an
X.509 certificate used as public authentication credential for that
trust anchor, by means of the CWT confirmation method "x5chain"
defined in [I-D.ietf-ace-edhoc-oscore-profile].
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Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Max-Age: 3600
Payload:
{
/ access_token / 1 : b64'SlAV32hk'/...
(remainder of CWT omitted for brevity;
CWT contains the client's RPK in the "cnf" claim)/,
/ expires_in / 2 : 3600,
e'anchor_cnf' : [
{
e'x5chain' : h'308201363081dea003020102020301f50d30
0a06082a8648ce3d04030230163114301206
035504030c0b524643207465737420434130
1e170d3230303130313030303030305a170d
3231303230323030303030305a3022312030
1e06035504030c1730312d32332d34352d46
462d46452d36372d38392d41423059301306
072a8648ce3d020106082a8648ce3d030107
03420004b1216ab96e5b3b3340f5bdf02e69
3f16213a04525ed44450b1019c2dfd3838ab
ac4e14d86c0983ed5e9eef2448c6861cc406
547177e6026030d051f7792ac206a30f300d
300b0603551d0f040403020780300a06082a
8648ce3d04030203470030440220445d798c
90e7f500dc747a654cec6cfa6f037276e14e
52ed07fc16294c84660d02205a33985dfbd4
bfdd6d4acf3804c3d46ebf3b7fa62640674f
c0354fa056dbaea6'
}
]
}
Figure 8: Example of Access Token Response with an access token
bound to an asymmetric key, using the "anchor_cnf" parameter.
3.5. rev_aud
This section defines the additional "rev_aud" parameter. The
parameter can be used in an Access Token Request sent by C to the
token endpoint at the AS, as well as in the successful Access Token
Response sent as reply by the AS.
* The "rev_aud" parameter is OPTIONAL in an Access Token Request.
The presence of this parameter indicates that C wishes the
requested access token to specify additional access rights. These
are intended for the access token's audience to access protected
resources at C as the access token's reverse audience.
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This parameter specifies such a reverse audience as a text string
identifier of C. When the Access Token Request is encoded in
CBOR, the value of this parameter is encoded as a CBOR text
string.
* The "rev_aud" parameter is OPTIONAL in an Access Token Response.
If present, it has the same meaning and encoding that it has in
the Access Token Request.
Fundamentally, this parameter has the same semantics of the "aud"
parameter used in the ACE framework, with the difference that it
conveys an identifier of C as a host of protected resources to
access, according to the access rights granted as reverse scope to
the audience of the access token issued by the AS.
The use of this parameter is further detailed in Section 4.
3.6. rev_scope
This section defines the additional "rev_scope" parameter. The
parameter can be used in an Access Token Request sent by C to the
token endpoint at the AS, as well as in the successful Access Token
Response sent as reply by the AS.
* The "rev_scope" parameter is OPTIONAL in an Access Token Request.
The presence of this parameter indicates that C wishes the
requested access token to specify additional access rights. These
are intended for the access token's audience to access protected
resources at C as the access token's reverse audience.
This parameter specifies such access rights as a reverse scope.
When the Access Token Request is encoded in CBOR, the value of
this parameter is encoded as a CBOR text string or a CBOR byte
string.
* The "rev_scope" parameter is OPTIONAL in an Access Token Response.
If present, this parameter specifies the access rights that the AS
has actually granted as a reverse scope to the access token's
audience, for accessing protected resources at C as the access
token's reverse audience.
Fundamentally, this parameter has the same semantics of the "scope"
parameter used in ACE framework, with the difference that it conveys
an identifier of C as a host of protected resources to access,
according to the access rights granted as reverse scope to the
audience of the access token issued by the AS.
The use of this parameter is further detailed in Section 4.
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4. Bidirectional Access Control
In some deployments, two devices DEV1 and DEV2 might wish to access
each other's protected resources. This can clearly be achieved by
means of two separate access tokens, each of which is used to enforce
access control in one direction. That is:
* A first access token is requested by and issued to DEV1, for
accessing protected resources at DEV2. With respect to this
access token, DEV1 is an ACE Client, while DEV2 is an ACE RS.
* A second access token is requested by and issued to DEV2, for
accessing protected resources at DEV1. With respect to this
access token, DEV2 is an ACE Client, while DEV1 is an ACE RS.
This section defines how to enforce such a bidirectional access
control by means of a single access token, which is requested by and
issued to a device DEV1 acting as ACE Client. In particular:
* The access token expresses access rights according to which the
requesting ACE Client DEV1 can access protected resources hosted
at the ACE RS DEV2.
For this first direction of access control, the target DEV2 is
specified by means of the "aud" parameter and the corresponding
access token claim, while the access rights are specified by means
of the "scope" parameter and the corresponding access token claim.
This is the original, primary direction of access control, where
the ACE Client DEV1 that requests the access token wishes access
rights to access protected resources at the ACE RS DEV2.
* The same access token additionally expresses access rights
according to which the ACE RS DEV2 can access protected resources
hosted at the ACE Client DEV1.
For this second direction of access control, the target DEV1 is
specified by means of the "rev_aud" parameter defined in
Section 3.5 and the corresponding access token claim defined in
this section, while the access rights are specified by means of
the "rev_scope" parameter defined in Section 3.6 and the
corresponding access token claim defined in this section.
This is the new, secondary direction of access control, where the
ACE Client DEV1 that requests the access token also wishes access
rights for the ACE RS DEV2 to access resources at DEV1.
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Clearly, this requires the ACE Client DEV1 to also act as CoAP
server, and the ACE RS DEV2 to also act as CoAP client.
Like for the original case with a single access control direction,
the access token is uploaded to the ACE RS DEV2, which processes the
access token as per Section 5.10 of [RFC9200] and according to the
transport profile of ACE used by DEV1 and DEV2.
The protocol workflow is detailed in the following Section 4.1 and
Section 4.2, in case only one Authorization Server or two
Authorization Servers are involved, respectively.
4.1. Scenario with One Authorization Server
As shown in Figure 9, this section considers a scenario with a single
Authorization Server AS. Both devices DEV1 and DEV2 are registered
at AS, and each of them with permissions to access protected
resources at the other device. In the following, DEV1 acts as ACE
Client by requesting an access token from AS.
- DEV1 is registered as: +----+
- Device authorized to access DEV2; and | |
- Device that can be accessed by DEV2 | |
| |
- DEV2 is registered as: | AS |
- Device that can be accessed by DEV1; and | |
- Device authorized to access DEV1 | |
| |
+----+
^
|
|
|
v
DEV2 DEV1
+----+ +---+
| RS | <--------------------------------------> | C |
+----+ +---+
Figure 9: Bidirectional access control with one Authorization Server.
4.1.1. Access Token Request
As to the Access Token Request that DEV1 sends to AS, the following
applies.
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* The "aud" and "scope" parameters are used as defined in [RFC9200],
and according to the transport profile of ACE used by DEV1 and
DEV2.
In particular, "aud" specifies an identifier of DEV2, while
"scope" specifies access rights that DEV1 wishes to obtain for
accessing protecting resources at DEV2.
That is, the two parameters pertain to the primary direction of
access control.
* The "req_cnf" parameter defined in [RFC9201] can be included.
When present, it specifies the key that DEV1 wishes to bind to the
requested access token.
* The "rev_aud" and "rev_scope" parameters defined in Section 3.5
and Section 3.6 can be included.
In particular, "rev_aud" specifies an identifier of DEV1, while
"rev_scope" specifies access rights that DEV1 wishes for DEV2 to
obtain for accessing protecting resources at DEV1.
That is, the two parameters pertain to the secondary direction of
access control.
If DEV1 wishes that the requested access token also provides DEV2
with access rights pertaining to the secondary direction of access
control, then the Access Token Request has to include at least one of
the two parameters "rev_aud" and "rev_scope".
4.1.2. Access Token Response
When receiving an Access Token Request that includes at least one of
the two parameters "rev_aud" and "rev_scope", AS processes it as
defined in Section 5.2 of [RFC9200], with the following additions:
* If the Access Token Request includes the "rev_scope" parameter but
not the "rev_aud" parameter, then AS assumes the identifier of
DEV1 to be the default one, if any is defined.
* If the Access Token Request includes the "rev_aud" parameter but
not the "rev_scope" parameter, then AS assumes the access rights
requested for DEV2 to access DEV1 to be the default ones, if any
are defined.
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* AS checks whether the access rights requested for DEV2 as reverse
scope can be at least partially granted, in accordance with the
installed access policies pertaining to the access to protected
resources at DEV1 from DEV2.
That is, AS performs the same evaluation that it would perform if
DEV2 sent an Access Token Request as an ACE Client, with the
intent to access protected resources at DEV1 as an ACE RS.
It is REQUIRED that such evaluation succeeds, in order for AS to
issue an access token and reply to DEV1 with a successful Access
Token Response.
As to the successful Access Token Response that AS sends to DEV1, the
following applies.
* The "aud" and "scope" parameters are used as defined in [RFC9200],
and according to the transport profile of ACE used by DEV1 and
DEV2.
In particular, "aud" specifies an identifier of DEV2, while
"scope" specifies the access rights that AS has granted to DEV1
for accessing protecting resources at DEV2.
The "scope" parameter has to be present if: i) it was present in
the Access Token Request, and the access rights granted to DEV1
are different from the requested ones; or ii) it was not present
in the Access Token Request, and the access rights granted to DEV1
are different from the default ones.
If the "scope" parameter is not present, then the granted access
rights are the same as those requested by the "scope" parameter in
the Access Token Request if present therein, or the default access
rights otherwise.
* The "rs_cnf" parameter defined in [RFC9201] can be included. When
present, it specifies information about the public key that DEV2
uses to authenticate.
* The "rev_aud" parameter defined in Section 3.5 can be included,
and specifies an identifier of DEV1.
If the "rev_aud" parameter is present in the Access Token Response
and it was also present in the Access Token Request, then the
parameter in the Access Token Response MUST have the same value
specified by the parameter in the Access Token Request.
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* The "rev_scope" parameter defined in Section 3.6 can be included,
and specifies access rights that AS has granted to DEV2 for
accessing protecting resources at DEV1.
The "rev_scope" parameter MUST be present if: i) it was present in
the Access Token Request, and the access rights granted to DEV2
are different from the requested ones; or ii) it was not present
in the Access Token Request, and the access rights granted to DEV2
are different from the default ones.
If the "rev_scope" parameter is not present, then the access
rights granted to DEV2 are the same as those requested by the
"rev_scope" parameter in the Access Token Request if present
therein, or the default access rights otherwise.
The issued access token MUST include information about the reverse
audience and reverse scope pertaining to the secondary access control
direction. In particular:
* The access token MUST contain a claim specifying the identifier of
DEV1.
If the Access Token Response includes the "rev_aud" parameter,
then the claim specifies the same information conveyed by that
parameter.
If this is not the case, then the claim specifies the same
information conveyed by the "rev_aud" parameter of the Access
Token Request, if included therein, or the default identifier of
DEV1 otherwise.
When CWTs are used as access tokens, this information MUST be
transported in the "rev_aud" claim defined in Section 8.4.
* The access token MUST contain a claim specifying the access rights
that AS has granted to DEV2 for accessing protecting resources at
DEV1.
If the Access Token Response includes the "rev_scope" parameter,
then the claim specifies the same information conveyed by that
parameter.
If this is not the case, then the claim specifies the same
information conveyed by the "rev_scope" parameter of the Access
Token Request, if included therein, or the default access rights
for DEV2 to access DEV1 otherwise.
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When CWTs are used as access tokens, this information MUST be
transported in the "rev_scope" claim, defined in Section 8.4.
4.1.3. Access to Protected Resources
As to the secure communication association between DEV1 and DEV2, its
establishment and maintenance does not deviate from what is defined
in the transport profile of ACE used by DEV1 and DEV2.
Furthermore, communications between DEV1 and DEV2 MUST rely on such
secure communication association for both directions of access
control, i.e., when DEV1 accesses protected resources at DEV2 and
vice versa.
After having received a successful Access Token Response from AS,
DEV1 MUST maintain and enforce the information about the access
rights granted to DEV2 and pertaining the secondary access control
direction.
In particular, DEV1 MUST prevent DEV2 from accessing protected
resources at DEV1, in case access requests from DEV2 are not
authorized as per the reverse scope specified by the issued access
token, or after having purged the issued access token (e.g.,
following its expiration of revocation).
4.2. Scenario with Two Authorization Servers
TBD
4.3. Practical Considerations
When enforcing bidirectional access control by means of a single
access token, the following considerations hold.
* The access token can be uploaded to the ACE RS DEV2 by the ACE
Client per the original ACE workflow, or by the AS that has issued
the access token per the new ACE workflow defined in Section 2.
* Since the access token is requested by the ACE Client DEV1, only
DEV1 can request for a new access token in the same token series,
in order to dynamically update the access rights concerning its
own access to protected resources hosted by DEV2 (on the primary
access control direction) and/or the access rights concerning the
access of DEV2 to access protected resources hosted by DEV1 (on
the secondary access control direction).
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5. Updated Requirements on Profiles
Appendix C of [RFC9200] compiles a list of requirements on the
profiles of ACE. This document amends two of those requirements as
follows.
The text of the fifth requirement
| Specify the security protocol the client and RS must use to
| protect their communication (e.g., OSCORE or DTLS). This must
| provide encryption and integrity and replay protection
| (Section 5.8.4.3).
is replaced by the following text:
| Specify the security protocol the client and RS must use to
| protect their communication (e.g., OSCORE or DTLS). In
| combination with the used communication protocol, this must
| provide encryption, integrity and replay protection, and a binding
| between requests and responses (Section 5.8.4.3 and Section 6.5).
The text of the tenth requirement
| Specify the communication and security protocol for interactions
| between the client and AS. This must provide encryption,
| integrity protection, replay protection, and a binding between
| requests and responses (Sections 5 and 5.8).
is replaced by the following text:
| Specify the communication and security protocol for interactions
| between the client and AS. The combined use of those protocols
| must provide encryption, integrity protection, replay protection,
| and a binding between requests and responses (Sections 5 and 5.8).
At the time of writing, all the profiles of ACE that are published as
RFC (i.e., [RFC9202][RFC9203][RFC9431]) already comply with the two
updated requirements as formulated above.
6. Updated Payload Format of Error Responses
This section deprecates the original payload format of error
responses conveying an error code, when CBOR is used to encode
message payloads in the ACE framework. That format is referred to,
e.g., when defining the error responses of Sections 5.8.3 and 5.9.3
of [RFC9200].
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Also, this section defines a new payload format that allows such
error responses to convey an error code together with further error-
specific information, according to the problem-details format
specified in [RFC9290].
Such error responses MUST have Content-Format set to application/
concise-problem-details+cbor. The payload of these error responses
MUST be a CBOR map specifying a Concise Problem Details data item
(see Section 2 of [RFC9290]). The CBOR map is formatted as follows.
* It MUST include the Custom Problem Detail entry "ace-error"
registered in Section 8.5 of this document.
This entry is formatted as a CBOR map including only one field,
namely "error-code". The map key for "error-code" is the CBOR
unsigned integer with value 0. The value of "error-code" is a
CBOR integer specifying the error code associated with the
occurred error. This value is taken from the "CBOR Value" column
of the "OAuth Error Code CBOR Mappings" registry
[ACE.OAuth.Error.Code.CBOR.Mappings].
The new payload format MUST use the field "error-code" in order to
convey the same information that the original payload format
conveys through the "error" parameter (see, e.g., Sections 5.8.3
and 5.9.3 of [RFC9200]).
The CDDL notation [RFC8610] of the "ace-error" entry is given
below.
ace-error = {
&(error-code: 0) => int
}
* It MAY include further Standard Problem Detail entries or Custom
Problem Detail entries (see [RFC9290]). The following Standard
Problem Detail entries are of particular relevance for the ACE
framework.
- "detail" (map key -2): its value is a CBOR text string that
specifies a human-readable, diagnostic description of the
occurred error (see Section 2 of [RFC9290]).
The diagnostic text is intended for software engineers as well
as for device and network operators, in order to aid debugging
and provide context for possible intervention. The diagnostic
message SHOULD be logged by the sender of the error response.
The entry "detail" is unlikely relevant in an unattended setup
where human intervention is not expected.
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The new payload format MUST use the Standard Problem Detail
entry "detail" in order to convey the same information that the
original payload format conveys through the "error_description"
parameter (see, e.g., Sections 5.8.3 and 5.9.3 of [RFC9200]).
- "instance" (map key -3): its value is a URI reference
identifying the specific occurrence of the error (see Section 2
of [RFC9290]).
The new payload format MUST use the Standard Problem Detail
entry "instance" in order to convey the same information that
the original payload format conveys through the "error_uri"
parameter (see, e.g., Sections 5.8.3 and 5.9.3 of [RFC9200]).
An example of error response using the problem-details format is
shown in Figure 10.
Header: Bad Request (Code=4.00)
Content-Format: application/concise-problem-details+cbor
Payload:
{
/ title / -1 : "Incompatible ACE profile",
/ detail / -2 : "The RS supports only the OSCORE profile",
e'ace-error': {
/ error_code / 0: 8 / incompatible_ace_profiles /
}
}
Figure 10: Example of Error Response with Problem Details.
Note to RFC Editor: In the figure above, please replace "TBD" with
the unsigned integer assigned as key value to the Custom Problem
Detail entry "ace-error" (see Section 8.5). Then, please delete this
paragraph.
When the ACE framework is used with CBOR for encoding message
payloads, the following applies.
* It is RECOMMENDED that Authorization Servers, Clients, and
Resource Servers support the payload format defined in this
section.
* Authorization Servers, Clients, and Resource Servers that support
the payload format defined in this section MUST use it when
composing an outgoing error response that conveys an error code.
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7. Security Considerations
The same security considerations from the ACE framework for
Authentication and Authorization [RFC9200] apply to this document,
together with those from the specifically used transport profile of
ACE, e.g., [RFC9202][RFC9203][RFC9431][I-D.ietf-ace-edhoc-oscore-prof
ile][I-D.ietf-ace-group-oscore-profile][RFC9431].
When using the problem-details format defined in [RFC9290] for error
responses, then the privacy and security considerations from Sections
4 and 5 of [RFC9290] also apply.
Editor's note: add more security considerations.
8. IANA Considerations
This document has the following actions for IANA.
Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]"
with the RFC number of this specification and delete this paragraph.
8.1. OAuth Parameters Registry
IANA is asked to add the following entries to the "OAuth Parameters"
registry.
* Name: "token_upload"
* Parameter Usage Location: token request and token response
* Change Controller: IETF
* Reference: [RFC-XXXX]
* Name: "token_hash"
* Parameter Usage Location: token response
* Change Controller: IETF
* Reference: [RFC-XXXX]
* Name: "rs_cnf2"
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* Parameter Usage Location: token response
* Change Controller: IETF
* Reference: [RFC-XXXX]
* Name: "aud2"
* Parameter Usage Location: token response
* Change Controller: IETF
* Reference: [RFC-XXXX]
* Name: "anchor_cnf"
* Parameter Usage Location: token response
* Change Controller: IETF
* Reference: [RFC-XXXX]
* Name: "rev_aud"
* Parameter Usage Location: token request and token response
* Change Controller: IETF
* Reference: [RFC-XXXX]
* Name: "rev_scope"
* Parameter Usage Location: token request and token response
* Change Controller: IETF
* Reference: [RFC-XXXX]
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8.2. OAuth Parameters CBOR Mappings Registry
IANA is asked to add the following entries to the "OAuth Parameters
CBOR Mappings" registry, following the procedure specified in
[RFC9200].
* Name: "token_upload"
* CBOR Key: TBD
* Value Type: unsigned integer
* Reference: [RFC-XXXX]
* Name: "token_hash"
* CBOR Key: TBD
* Value Type: unsigned integer
* Reference: [RFC-XXXX]
* Name: "rs_cnf2"
* CBOR Key: TBD
* Value Type: array
* Reference: [RFC-XXXX]
* Name: "aud2"
* CBOR Key: TBD
* Value Type: array
* Reference: [RFC-XXXX]
* Name: "anchor_cnf"
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* CBOR Key: TBD
* Value Type: array
* Reference: [RFC-XXXX]
* Name: "rev_aud"
* CBOR Key: TBD
* Value Type: text string
* Reference: [RFC-XXXX]
* Name: "rev_scope"
* CBOR Key: TBD
* Value Type: text string or byte string
* Reference: [RFC-XXXX]
8.3. JSON Web Token Claims Registry
IANA is asked to add the following entries to the "JSON Web Token
Claims" registry, following the procedure specified in [RFC7519].
* Claim Name: "rev_aud"
* Claim Description: The reverse audience of an access token
* Change Controller: IETF
* Reference: [RFC-XXXX]
* Claim Name: "rev_scope"
* Claim Description: The reverse scope of an access token
* Change Controller: IETF
* Reference: [RFC-XXXX]
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8.4. CBOR Web Token (CWT) Claims Registry
IANA is asked to add the following entries to the "CBOR Web Token
(CWT) Claims" registry, following the procedure specified in
[RFC8392].
* Claim Name: "rev_aud"
* Claim Description: The reverse audience of an access token
* JWT Claim Name: "rev_aud"
* Claim Key: TBD
* Claim Value Type: text string
* Change Controller: IETF
* Reference: Section 4 of [RFC-XXXX]
* Claim Name: "rev_scope"
* Claim Description: The reverse scope of an access token
* JWT Claim Name: "rev_scope"
* Claim Key: TBD
* Claim Value Type: text string or byte string
* Change Controller: IETF
* Reference: Section 4 of [RFC-XXXX]
8.5. Custom Problem Detail Keys Registry
IANA is asked to register the following entry in the "Custom Problem
Detail Keys" registry within the "Constrained RESTful Environments
(CoRE) Parameters" registry group.
* Key Value: TBD
* Name: ace-error
* Brief Description: Carry ACE [RFC9200] problem details in a
Concise Problem Details data item.
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* Change Controller: IETF
* Reference: Section 6 of [RFC-XXXX]
9. References
9.1. Normative References
[ACE.OAuth.Error.Code.CBOR.Mappings]
IANA, "OAuth Error Code CBOR Mappings",
<https://www.iana.org/assignments/ace/ace.xhtml#oauth-
error-code-cbor-mappings>.
[I-D.ietf-ace-edhoc-oscore-profile]
Selander, G., Mattsson, J. P., Tiloca, M., and R. Höglund,
"Ephemeral Diffie-Hellman Over COSE (EDHOC) and Object
Security for Constrained Environments (OSCORE) Profile for
Authentication and Authorization for Constrained
Environments (ACE)", Work in Progress, Internet-Draft,
draft-ietf-ace-edhoc-oscore-profile-04, 4 March 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-ace-
edhoc-oscore-profile-04>.
[I-D.ietf-ace-revoked-token-notification]
Tiloca, M., Palombini, F., Echeverria, S., and G. Lewis,
"Notification of Revoked Access Tokens in the
Authentication and Authorization for Constrained
Environments (ACE) Framework", Work in Progress, Internet-
Draft, draft-ietf-ace-revoked-token-notification-08, 24
June 2024, <https://datatracker.ietf.org/doc/html/draft-
ietf-ace-revoked-token-notification-08>.
[Named.Information.Hash.Algorithm]
IANA, "Named Information Hash Algorithm",
<https://www.iana.org/assignments/named-information/named-
information.xhtml>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <https://www.rfc-editor.org/rfc/rfc3629>.
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[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/rfc/rfc4648>.
[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/rfc/rfc6749>.
[RFC6920] Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B.,
Keranen, A., and P. Hallam-Baker, "Naming Things with
Hashes", RFC 6920, DOI 10.17487/RFC6920, April 2013,
<https://www.rfc-editor.org/rfc/rfc6920>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/rfc/rfc7252>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/rfc/rfc7519>.
[RFC7800] Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
Possession Key Semantics for JSON Web Tokens (JWTs)",
RFC 7800, DOI 10.17487/RFC7800, April 2016,
<https://www.rfc-editor.org/rfc/rfc7800>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259,
DOI 10.17487/RFC8259, December 2017,
<https://www.rfc-editor.org/rfc/rfc8259>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/rfc/rfc8392>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>.
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[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Definition Language (CDDL): A Notational Convention to
Express Concise Binary Object Representation (CBOR) and
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
June 2019, <https://www.rfc-editor.org/rfc/rfc8610>.
[RFC8747] Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", RFC 8747, DOI 10.17487/RFC8747, March
2020, <https://www.rfc-editor.org/rfc/rfc8747>.
[RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/rfc/rfc8949>.
[RFC9052] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Structures and Process", STD 96, RFC 9052,
DOI 10.17487/RFC9052, August 2022,
<https://www.rfc-editor.org/rfc/rfc9052>.
[RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053,
August 2022, <https://www.rfc-editor.org/rfc/rfc9053>.
[RFC9200] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments Using the OAuth 2.0 Framework
(ACE-OAuth)", RFC 9200, DOI 10.17487/RFC9200, August 2022,
<https://www.rfc-editor.org/rfc/rfc9200>.
[RFC9201] Seitz, L., "Additional OAuth Parameters for Authentication
and Authorization for Constrained Environments (ACE)",
RFC 9201, DOI 10.17487/RFC9201, August 2022,
<https://www.rfc-editor.org/rfc/rfc9201>.
[RFC9202] Gerdes, S., Bergmann, O., Bormann, C., Selander, G., and
L. Seitz, "Datagram Transport Layer Security (DTLS)
Profile for Authentication and Authorization for
Constrained Environments (ACE)", RFC 9202,
DOI 10.17487/RFC9202, August 2022,
<https://www.rfc-editor.org/rfc/rfc9202>.
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[RFC9203] Palombini, F., Seitz, L., Selander, G., and M. Gunnarsson,
"The Object Security for Constrained RESTful Environments
(OSCORE) Profile of the Authentication and Authorization
for Constrained Environments (ACE) Framework", RFC 9203,
DOI 10.17487/RFC9203, August 2022,
<https://www.rfc-editor.org/rfc/rfc9203>.
[RFC9290] Fossati, T. and C. Bormann, "Concise Problem Details for
Constrained Application Protocol (CoAP) APIs", RFC 9290,
DOI 10.17487/RFC9290, October 2022,
<https://www.rfc-editor.org/rfc/rfc9290>.
[RFC9430] Bergmann, O., Preuß Mattsson, J., and G. Selander,
"Extension of the Datagram Transport Layer Security (DTLS)
Profile for Authentication and Authorization for
Constrained Environments (ACE) to Transport Layer Security
(TLS)", RFC 9430, DOI 10.17487/RFC9430, July 2023,
<https://www.rfc-editor.org/rfc/rfc9430>.
[RFC9431] Sengul, C. and A. Kirby, "Message Queuing Telemetry
Transport (MQTT) and Transport Layer Security (TLS)
Profile of Authentication and Authorization for
Constrained Environments (ACE) Framework", RFC 9431,
DOI 10.17487/RFC9431, July 2023,
<https://www.rfc-editor.org/rfc/rfc9431>.
9.2. Informative References
[I-D.ietf-ace-group-oscore-profile]
Tiloca, M., Höglund, R., and F. Palombini, "The Group
Object Security for Constrained RESTful Environments
(Group OSCORE) Profile of the Authentication and
Authorization for Constrained Environments (ACE)
Framework", Work in Progress, Internet-Draft, draft-ietf-
ace-group-oscore-profile-01, 4 March 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-ace-
group-oscore-profile-01>.
Appendix A. Benefits for ACE Transport Profiles
For any transport profile of ACE, the following holds.
* The new ACE workflow defined in Section 2 is effectively possible
to use. This is beneficial for deployments where the
communication leg between C and the RS is constrained, but the
communication leg between the AS and RS is not.
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* When the new ACE workflow is used, the "token_upload" parameter
defined in Section 3.1 is used:
- To inform the AS about C opting in to use the new ACE workflow.
- To request the AS that the follow-up successful Access Token
Response will have to include certain information, in case the
AS has successfully uploaded the access token to the RS.
- To inform C that the AS has attempted to upload the issued
access token to the RS, specifying whether the uploading has
succeeded or failed.
* When the new ACE workflow is used, it remains possible for C to
always obtain the issued access token from the AS.
That is, by specifying the value 2 for the "token_upload"
parameter in the Access Token Request, C will ensure to receive
the access token from the AS, even in case the AS successfully
uploads the access token to the RS on behalf of C.
This is useful in transport profiles of ACE where C can re-upload
the same Access Token to the RS by itself, e.g., in order to
perform a key update like defined for the OSCORE profile
[RFC9203].
A.1. DTLS Profile
When the RPK mode of the DTLS profile is used (see Section 3.2 of
[RFC9202]), it becomes possible for the AS to effectively issue an
access token intended to an audience that includes multiple RSs.
This is enabled by the parameters "rs_cnf2" and "aud2" defined in
Section 3.3, as well as by the "anchor_cnf" parameter defined in
Section 3.4. This seamlessly applies also if the profile uses
Transport Layer Security (TLS) [RFC8446], as defined in [RFC9430].
A.2. EDHOC and OSCORE Profile
When the EDHOC and OSCORE profile is used
[I-D.ietf-ace-edhoc-oscore-profile], it becomes possible for the AS
to effectively issue an access token intended to an audience that
includes multiple RSs. This is enabled by the parameters "rs_cnf2"
and "aud2" defined in Section 3.3, as well as by the "anchor_cnf"
parameter defined in Section 3.4.
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Appendix B. Open Points
B.1. New Workflow
The following discusses open points related to the use of the new ACE
workflow defined in Section 2.
B.1.1. Allow the Dynamic Update of Access Rights
In some profiles of ACE, C can request a new access token to update
its access rights, while preserving the same secure association with
the RS. The new access token supersedes the current one stored at
the RS, as they are both part of the same token series.
When using the original ACE workflow, C uploads the new access token
to the RS by protecting the message exchange through the secure
association with the RS. This allows the RS to determine that the
upload of such access token is for updating the access rights of C.
When using the new ACE workflow, the AS uploads the new access token
to the RS also when an update of access rights for C is to be
performed. This message exchange would be protected through the
secure association between the AS and the RS. However, this secure
association does not help the RS retrieve the stored access token to
supersede, as that is rather bound to the secure association with C.
In order for the new ACE workflow to also allow the dynamic update of
access rights, it is required that the new access token updating the
access rights of C includes an explicit indication for the RS. Such
an indication can point the RS to the token series in question (hence
to the current access token to supersede), irrespective of the secure
association used to protect the token uploading.
In some profiles of ACE, such an indication is in fact already
present in issued access tokens:
* In the PSK mode of the DTLS profile [RFC9202], the token series is
indicated by the "kid" parameter within the "cnf" claim of the new
access token. This has the same value of the "kid" parameter in
the COSE_Key within the "cnf" claim from the first access token of
the token series.
* In the OSCORE profile [RFC9203], the token series is indicated by
the "kid" parameter within the "cnf" claim of the new access
token. This has the same value of the "id" parameter in the
OSCORE_Input_Material object within the "cnf" claim from the first
access token of the token series.
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* In the EDHOC and OSCORE profile
[I-D.ietf-ace-edhoc-oscore-profile], the token series is indicated
by the "kid" parameter within the "cnf" claim of the new access
token. This has the same value of the "id" parameter in the
EDHOC_Information object within the "cnf" claim from the first
access token of the token series.
In the three cases above, the update of access rights is possible
because there is a value used as de facto "token series ID". This
value does not change throughout the lifetime of a token series, and
it is used to associate the new access token with the previous one in
the same series to be superseded.
Such a token series ID is required to have a unique value from a
namespace/pool that the AS exclusively controls. This is in fact
what happens in the profiles of ACE above, where the AS is the entity
creating the mentioned objects or COSE Key included in the first
access token of a token series.
However, this may generally not hold and it is not what happens in
other known cases, i.e., the DTLS profile in RPK mode [RFC9203] and
the Group OSCORE profile [I-D.ietf-ace-group-oscore-profile]. At the
moment, the dynamic update of access rights is not possible for
those, _neither in the original nor in the new ACE workflow_.
In order to make the update of access rights possible also for such
cases, as well as both in the original and in the new ACE workflow,
those cases can rely on a new "token_series_id" parameter and
corresponding "token_series_id" claim (see Appendix B.2), which
specify a unique identifier of the token series which an access token
belongs to.
As to existing profiles of ACE, the above has no intention to change
the current behavior when the update of access rights occurs,
irrespective of the used ACE workflow and especially when using the
original workflow.
If future profiles rely on a construction where the AS creates the
object or the key included in the "cnf" claim of the first access
token in a token series, and a unique ID generated by the AS is
included in such object or key, then that ID must be used as de facto
"token series ID", rather than the new "token_series_id" parameter.
Even though a "token series ID" provides an explicit indication for
recognizing a stored access token as belonging to an ongoing token
series, such a process might still be prone to ambiguities. For
example, the RS might have deleted a stored access token due to
memory limitations. This effectively terminates the corresponding
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token series, which is however impractical for the RS to remember
indefinitely. Consequently, if the AS uploads to the RS a new access
token belonging to the same token series, the RS would erroneously
interpret it to be the first access token of a new series. This can
be avoided by relying on a new "updated_rights" parameter, which the
AS can include in a POST request to the /authz-info endpoint when
uploading to the RS an access token for dynamically updating the
access rights of C (see Appendix B.2).
B.1.2. Ensure Applicability to Any ACE Profile
Some profiles of ACE require that C and the RS generate information
to be exchanged when uploading the access token.
For example, in the OSCORE profile [RFC9203], C and the RS exchange
the nonces N1 and N2 together with their OSCORE Recipient IDs ID1 and
ID2, when uploading to the RS the first access token of a token
series, as well as when re-uploading any access token (e.g., in order
to perform a key update).
Evidently, using the new ACE workflow prevents C and the RS from
directly performing the required exchanges above, since the uploading
of the access token does not rely on a direct interaction between C
and the RS like in the original ACE workflow. For some profiles of
ACE, this may prevent the use of the new ACE workflow altogether.
This issue can be solved by having the AS acting as intermediary also
for the exchange of C- and RS-generated information, by relying on
two new parameters "to_rs" and "from_rs" (see Appendix B.2). In
particular, C can use "to_rs" for providing the AS with C-generated
information, to be relayed to the RS when uploading the access token.
Also, the RS can use "from_rs" for providing the AS with RS-generated
information when replying to the token uploading, and to be relayed
to C.
With reference to the two cases mentioned above, "to_rs" can specify
the nonce N1 generated by C, while "from_rs" can specify the nonce N2
generated by the RS.
B.2. Further New Parameters to Consider
The following discusses possible, further new parameters that can be
defined for addressing the open points raised earlier in Appendix B.
* "token_series_id" - This parameter specifies the unique identifier
of a token series, thus ensuring that C can dynamically update its
access rights, irrespective of the used ACE workflow (see
Appendix B.1.1).
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When issuing the first access token of a token series, the AS
specifies this parameter in the Access Token Response to C, with
value TS_ID. Also, the AS includes a "token_series_id" claim with
the same value in the access token.
When C requests a new access token in the same tokes series for
dynamically updating its access rights, C specifies TS_ID as value
of the "token_series_id" parameter of the Access Token Request,
which MUST omit the "req_cnf" parameter (see Section 3.1 of
[RFC9201]). The AS specifies the same value within the
"token_series_id" claim of the new access token.
When this parameter is used, the information about the token
series in question has to be specified in that parameter and in
the corresponding token claim. Instead, the "req_cnf" parameter
and the "cnf" claim are used for their main purpose, i.e., for
specifying the public authentication credential of the Client, by
value or by reference.
If a profile of ACE can use or is already using a different
parameter/claim as de-facto identifier of the token series, then
that profile will continue to do so, and will not use this new
"token_series_id" parameter.
* "updated_rights" - When using the new ACE workflow and issuing an
access token for dynamically updating the access rights of C, the
AS specifies this parameter in the request sent to the RS for
uploading the access token on behalf of C (see Appendix B.1.1).
This parameter encodes the CBOR simple value true (0xf5).
* "to_rs" - When using the new ACE workflow, this parameter
specifies C-generated information that, according to the used
profile of ACE, C has to provide to the RS together with the
access token if using the original ACE workflow. This allows the
AS to relay such information to the RS upon uploading the access
token on behalf of C (see Appendix B.1.2).
First, C specifies this parameter in the Access Token Request sent
to the AS. Then, the AS specifies this parameter in the request
to the RS sent for uploading the access token on behalf of C, by
simply relaying the value received from C. The used profile of
ACE has to define the detailed content and semantics of the
information specified in the parameter value.
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* "from_rs" - When using the new ACE workflow, this parameter
specifies RS-generated information that, according to the used
profile of ACE, the RS has to provide to C after the uploading of
an access token if using the original ACE workflow. This allows
the AS to relay such information to C after having uploaded the
access token on behalf of C (see Appendix B.1.2).
First, the RS specifies this parameter in the response sent to the
AS, after the upload of an access token through a request from the
AS. Then, the AS specifies this parameter in the Access Token
Response to C, by simply relaying the value received from the RS.
The used profile of ACE has to define the detailed content and
semantics of the information specified in the parameter value.
Appendix C. CDDL Model
This section is to be removed before publishing as an RFC.
; OAuth Parameters CBOR Mappings
token_upload = 48
token_hash = 49
aud_2 = 50
rs_cnf_2 = 51
anchor_cnf = 52
rev_aud_param = 53
rev_scope_param = 54
; CBOR Web Token (CWT) Claims
rev_aud_claim = 42
rev_scope_claim = 43
; CWT Confirmation Methods
x5chain = 5
; Custom Problem Detail Keys Registry
ace-error = 2
Figure 11: CDDL model
Appendix D. Document Updates
This section is to be removed before publishing as an RFC.
D.1. Version -01 to -02
* CBOR diagnostic notation uses placeholders from a CDDL model.
* Note on the new workflow supporting also non-ACE Clients.
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* Revised semantics of the "token_upload" parameter.
* Defined the new "token_hash" parameter.
* First definition of bidirectional access control through a single
access token.
* Revised and extended considerations and next steps in appendices.
* Clarifications and editorial improvements.
D.2. Version -00 to -01
* Definition of the "token series" moved to the "Terminology"
section.
* Clarifications and fixes on using parameters in messages.
* Amended two of the requirements on profiles of the framework.
* The Client has to opt-in for using the alternative workflow.
* Parameter "token_uploaded" renamed to "token_upload".
* Updated format of error response payload to use RFC 9290.
* Security considerations inherited from other documents.
* Editorial fixes and improvements.
Acknowledgments
The authors sincerely thank Christian Amsüss, Rikard Höglund, and
Dave Robin for their comments and feedback.
This work was supported by the Sweden's Innovation Agency VINNOVA
within the EUREKA CELTIC-NEXT project CYPRESS; and by the H2020
project SIFIS-Home (Grant agreement 952652).
Authors' Addresses
Marco Tiloca
RISE AB
Isafjordsgatan 22
SE-16440 Kista
Sweden
Email: marco.tiloca@ri.se
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Göran Selander
Ericsson AB
Torshamnsgatan 23
SE-16440 Stockholm Kista
Sweden
Email: goran.selander@ericsson.com
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