Additional OAuth Parameters for Authorization in Constrained Environments (ACE)
draft-ietf-ace-oauth-params-16
| Document | Type | Active Internet-Draft (ace WG) | ||
|---|---|---|---|---|
| Author | Ludwig Seitz | |||
| Last updated | 2021-09-15 (latest revision 2021-09-07) | |||
| Stream | Internet Engineering Task Force (IETF) | |||
| Intended RFC status | Proposed Standard | |||
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| Responsible AD | Benjamin Kaduk | |||
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| Details | ||||
ACE Working Group L. Seitz
Internet-Draft Combitech
Intended status: Standards Track 7 September 2021
Expires: 11 March 2022
Additional OAuth Parameters for Authorization in Constrained
Environments (ACE)
draft-ietf-ace-oauth-params-16
Abstract
This specification defines new parameters and encodings for the OAuth
2.0 token and introspection endpoints when used with the framework
for authentication and authorization for constrained environments
(ACE). These are used to express the proof-of-possession key the
client wishes to use, the proof-of-possession key that the
Authorization Server has selected, and the key the Resource Server
uses to authenticate to the client.
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
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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 11 March 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Parameters for the Token Endpoint . . . . . . . . . . . . . . 3
3.1. Client-to-AS Request . . . . . . . . . . . . . . . . . . 3
3.2. AS-to-Client Response . . . . . . . . . . . . . . . . . . 4
4. Parameters for the Introspection Endpoint . . . . . . . . . . 6
5. Confirmation Method Parameters . . . . . . . . . . . . . . . 7
6. CBOR Mappings . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Requirements when using asymmetric keys . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 9
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10.1. OAuth Parameter Registration . . . . . . . . . . . . . . 9
10.2. OAuth Parameters CBOR Mappings Registration . . . . . . 9
10.3. OAuth Token Introspection Response CBOR Mappings
Registration . . . . . . . . . . . . . . . . . . . . . . 10
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
12.1. Normative References . . . . . . . . . . . . . . . . . . 10
12.2. Informative References . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
The Authentication and Authorization for Constrained Environments
(ACE) specification [I-D.ietf-ace-oauth-authz] requires some new
parameters for interactions with the OAuth 2.0 [RFC6749] token and
introspection endpoints, as well as some new claims to be used in
access tokens. These parameters and claims can also be used in other
contexts and have therefore been put into a dedicated document, to
facilitate their use in a manner independent of
[I-D.ietf-ace-oauth-authz].
Note that although all examples are shown in Concise Binary Object
Representation (CBOR) [RFC8949], JSON [RFC8259] MAY be used as an
alternative for HTTP-based communications, as specified in
[I-D.ietf-ace-oauth-authz].
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2. 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 assumed to be familiar with the terminology from
[I-D.ietf-ace-oauth-authz], especially the terminology for entities
in the architecture such as client (C), resource server (RS) and
authorization server (AS).
Terminology from [RFC8152] is used in the examples, especially
COSE_Key defined in section 7 of [RFC8152].
Note that the term "endpoint" is used here following its OAuth 2.0
[RFC6749] definition, which is to denote resources such as token and
introspection at the AS and authz-info at the RS. The Constrained
Application Protocol (CoAP) [RFC7252] definition, which is "An entity
participating in the CoAP protocol" is not used in this
specification.
3. Parameters for the Token Endpoint
This section defines additional parameters for the interactions with
the token endpoint in the ACE framework [I-D.ietf-ace-oauth-authz].
3.1. Client-to-AS Request
This section defines the "req_cnf" parameter allowing clients to
request a specific proof-of-possession key in an access token from a
token endpoint in the ACE framework [I-D.ietf-ace-oauth-authz]:
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req_cnf
OPTIONAL. This field contains information about the key the
client would like to bind to the access token for proof-of-
possession. It is RECOMMENDED that an AS rejects a request
containing a symmetric key value in the 'req_cnf' field
(kty=Symmetric), since the AS is expected to be able to generate
better symmetric keys than a constrained client (Note: this does
not apply to key identifiers referencing a symmetric key). The AS
MUST verify that the client really is in possession of the
corresponding key. Profiles of [I-D.ietf-ace-oauth-authz] using
this specification MUST define the proof-of-possession method used
by the AS, if they allow clients to use this request parameter.
Values of this parameter 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.
Figure 1 shows a request for an access token using the "req_cnf"
parameter to request a specific public key as proof-of-possession
key. The content is displayed in CBOR diagnostic notation, without
abbreviations and with line-breaks for better readability.
Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: "application/ace+cbor"
Payload:
{
"req_cnf" : {
"COSE_Key" : {
"kty" : "EC2",
"kid" : h'11',
"crv" : "P-256",
"x" : h'BAC5B11CAD8F99F9C72B05CF4B9E26D24
4DC189F745228255A219A86D6A09EFF',
"y" : h'20138BF82DC1B6D562BE0FA54AB7804A3
A64B6D72CCFED6B6FB6ED28BBFC117E'
}
}
}
Figure 1: Example request for an access token bound to an
asymmetric key.
3.2. AS-to-Client Response
This section defines the following additional parameters for an AS
response to a request to the token endpoint:
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cnf
REQUIRED if the token type is "pop" and a symmetric key is used.
MAY be present for asymmetric proof-of-possession keys. This
field contains the proof-of-possession key that the AS selected
for the token. Values of this parameter 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. See Section 5 for additional discussion
of the usage of this parameter.
rs_cnf
OPTIONAL if the token type is "pop" and asymmetric keys are used.
MUST NOT be present otherwise. This field contains information
about the public key used by the RS to authenticate. If this
parameter is absent, either the RS does not use a public key or
the AS knows that the RS can authenticate itself to the client
without additional information. Values of this parameter 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. See Section 5 for
additional discussion of the usage of this parameter.
Figure 2 shows an AS response containing a token and a "cnf"
parameter with a symmetric proof-of-possession key.
Header: Created (Code=2.01)
Content-Format: "application/ace+cbor"
Payload:
{
"access_token" : h'4A5015DF686428 ...
(remainder of CWT omitted for brevity;
CWT contains COSE_Key in the "cnf" claim)',
"cnf" : {
"COSE_Key" : {
"kty" : "Symmetric",
"kid" : h'DFD1AA97',
"k" : h'849B5786457C1491BE3A76DCEA6C427108'
}
}
}
Figure 2: Example AS response with an access token bound to a
symmetric key.
Figure 3 shows an AS response containing a token bound to a
previously requested asymmetric proof-of-possession key (not shown)
and a "rs_cnf" parameter containing the public key of the RS.
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Header: Created (Code=2.01)
Content-Format: "application/ace+cbor"
Payload:
{
"access_token" : h'D08343A1010AA1054D2A45DF6FBC5A5A ...
(remainder of CWT omitted for brevity)',
"rs_cnf" : {
"COSE_Key" : {
"kty" : "EC2",
"kid" : h'12',
"crv" : "P-256",
"x" : h'BCEE7EAAC162F91E6F330F5771211E220
B8B546C96589B0AC4AD0FD24C77E1F1',
"y" : h'C647B38C55EFBBC4E62E651720F002D5D
75B2E0C02CD1326E662BCA222B90416'
}
}
}
Figure 3: Example AS response, including the RS's public key.
4. Parameters for the Introspection Endpoint
This section defines the use of CBOR instead of JSON for the "cnf"
introspection response parameter specified in section 9.4 of
[RFC8705].
If CBOR is used instead of JSON in an interaction with the
introspection endpoint, the AS MUST use the parameter mapping
specified in Figure 5 and the value must follow the syntax of "cnf"
claim values from section 3.1 of [RFC8747].
Figure 4 shows an AS response to an introspection request including
the "cnf" parameter to indicate the proof-of-possession key bound to
the token.
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Header: Created (Code=2.01)
Content-Format: "application/ace+cbor"
Payload:
{
"active" : true,
"scope" : "read",
"aud" : "tempSensor4711",
"cnf" : {
"COSE_Key" : {
"kty" : "EC2",
"kid" : h'11',
"crv" : "P-256",
"x" : h'BAC5B11CAD8F99F9C72B05CF4B9E26D24
4DC189F745228255A219A86D6A09EFF',
"y" : h'20138BF82DC1B6D562BE0FA54AB7804A3
A64B6D72CCFED6B6FB6ED28BBFC117E'
}
}
}
Figure 4: Example introspection response.
5. Confirmation Method Parameters
The confirmation method parameters are used in
[I-D.ietf-ace-oauth-authz] as follows:
* "req_cnf" in the access token request C -> AS, OPTIONAL to
indicate the client's raw public key, or the key-identifier of a
previously established key between C and RS that the client wishes
to use for proof-of-possession of the access token.
* "cnf" in the token response AS -> C, OPTIONAL if using an
asymmetric key or a key that the client requested via a key
identifier in the request. REQUIRED if the client didn't specify
a "req_cnf" and symmetric keys are used. Used to indicate the
symmetric key generated by the AS for proof-of-possession of the
access token.
* "cnf" in the introspection response AS -> RS, REQUIRED if the
access token that was subject to introspection is a proof-of-
possession token, absent otherwise. Indicates the proof-of-
possession key bound to the access token.
* "rs_cnf" in the token response AS -> C, OPTIONAL to indicate the
public key of the RS, if it uses one to authenticate itself to the
client and the binding between key and RS identity is not
established through other means.
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Note that the COSE_Key structure in a confirmation claim or parameter
may contain an "alg" or "key_ops" parameter. If such parameters are
present, a client MUST NOT use a key that is incompatible with the
profile or proof-of-possession algorithm according to those
parameters. 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).
If an access token is issued for an audience that includes several
RS, the "rs_cnf" parameter MUST NOT be used, since the client cannot
determine for which RS the key applies. This document recommends to
specify a different endpoint that the client can use to acquire RS
authentication keys in such cases. The specification of such an
endpoint is out of scope for this document.
6. CBOR Mappings
If CBOR is used, the new parameters and claims defined in this
document MUST be mapped to CBOR types as specified in Figure 5, using
the given integer abbreviation for the map key.
/----------+----------+-------------------------------------\
| Name | CBOR Key | Value Type | Usage |
|----------+----------+-------------------------------------|
| req_cnf | TBD (4) | map | token request |
| cnf | TBD (8) | map | token response |
| cnf | TBD (8) | map | introspection response |
| rs_cnf | TBD (41) | map | token response |
\----------+----------+------------+------------------------/
Figure 5: CBOR mappings for new parameters and claims.
7. Requirements when using asymmetric keys
An RS using asymmetric keys to authenticate to the client MUST NOT
hold several different asymmetric key pairs, applicable to the same
authentication algorithm. For example when using DTLS, the RS MUST
NOT hold several asymmetric key pairs applicable to the same cipher
suite. The reason for this restriction is that the RS has no way of
determining which key to use before the client's identity is
established. Therefore authentication attempts by the RS could
randomly fail based on which key the RS selects, unless the algorithm
negotiation produces a unique choice of key pair for the RS.
8. Security Considerations
This document is an extension to [I-D.ietf-ace-oauth-authz]. All
security considerations from that document apply here as well.
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9. Privacy Considerations
This document is an extension to [I-D.ietf-ace-oauth-authz]. All
privacy considerations from that document apply here as well.
10. IANA Considerations
10.1. OAuth Parameter Registration
This section registers the following parameters in the "OAuth
Parameters" registry [IANA.OAuthParameters]:
* Name: "req_cnf"
* Parameter Usage Location: token request
* Change Controller: IETF
* Reference: Section 5 of [this document]
* Name: "rs_cnf"
* Parameter Usage Location: token response
* Change Controller: IETF
* Reference: Section 5 of [this document]
* Name: "cnf"
* Parameter Usage Location: token response
* Change Controller: IETF
* Reference: Section 5 of [this document]
10.2. OAuth Parameters CBOR Mappings Registration
This section registers the following parameter mappings in the "OAuth
Parameters CBOR Mappings" registry established in section 8.9. of
[I-D.ietf-ace-oauth-authz].
* Name: "req_cnf"
* CBOR key: TBD (suggested: 4)
* Value Type: map
* Reference: Section 3.1 of [this document]
* Original specification: [this document]
* Name: "cnf"
* CBOR key: TBD (suggested: 8)
* Value Type: map
* Reference: Section 3.2 of [this document]
* Original specification: [this document]
* Name: "rs_cnf"
* CBOR key: TBD (suggested: 41)
* Value Type: map
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* Reference: Section 3.2 of [this document]
* Original specification: [this document]
10.3. OAuth Token Introspection Response CBOR Mappings Registration
This section registers the following parameter mapping in the "OAuth
Token Introspection Response CBOR Mappings" registry established in
section 8.11. of [I-D.ietf-ace-oauth-authz].
* Name: "cnf"
* CBOR key: TBD (suggested: 8)
* Value Type: map
* Reference: Section 4 of [this document]
* Original specification: [RFC8705]
11. Acknowledgments
This document is a product of the ACE working group of the IETF.
Special thanks to Brian Campbell for his thorough review of this
document.
Ludwig Seitz worked on this document as part of the CelticNext
projects CyberWI, and CRITISEC with funding from Vinnova.
12. References
12.1. Normative References
[I-D.ietf-ace-oauth-authz]
Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and
H. Tschofenig, "Authentication and Authorization for
Constrained Environments (ACE) using the OAuth 2.0
Framework (ACE-OAuth)", Work in Progress, Internet-Draft,
draft-ietf-ace-oauth-authz-45, 29 August 2021,
<https://www.ietf.org/archive/id/draft-ietf-ace-oauth-
authz-45.txt>.
[IANA.OAuthParameters]
IANA, "OAuth Parameters",
<https://www.iana.org/assignments/oauth-parameters/oauth-
parameters.xhtml#parameters>.
[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/info/rfc2119>.
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[RFC6749] Hardt, D., Ed., "The OAuth 2.0 Authorization Framework",
RFC 6749, DOI 10.17487/RFC6749, October 2012,
<https://www.rfc-editor.org/info/rfc6749>.
[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/info/rfc7800>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
RFC 8152, DOI 10.17487/RFC8152, July 2017,
<https://www.rfc-editor.org/info/rfc8152>.
[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/info/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/info/rfc8259>.
[RFC8705] Campbell, B., Bradley, J., Sakimura, N., and T.
Lodderstedt, "OAuth 2.0 Mutual-TLS Client Authentication
and Certificate-Bound Access Tokens", RFC 8705,
DOI 10.17487/RFC8705, February 2020,
<https://www.rfc-editor.org/info/rfc8705>.
[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/info/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/info/rfc8949>.
12.2. Informative References
[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/info/rfc7252>.
Author's Address
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Ludwig Seitz
Combitech
Djäknegatan 31
SE-211 35 Malmö
Sweden
Email: ludwig.seitz@combitech.com
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