ACE Working Group L. Seitz
Internet-Draft RISE
Intended status: Standards Track November 17, 2019
Expires: May 20, 2020
Additional OAuth Parameters for Authorization in Constrained
Environments (ACE)
draft-ietf-ace-oauth-params-06
Abstract
This specification defines new parameters 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
whishes to use, the proof-of-possession key that the AS has selected,
and the key the RS should use to authenticate to the client.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 20, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
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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
3.3. The Resource Server Confirmation Claim . . . . . . . . . 5
4. Parameters for the Introspection Endpoint . . . . . . . . . . 6
4.1. AS-to-RS Response . . . . . . . . . . . . . . . . . . . . 6
5. Confirmation Method Parameters . . . . . . . . . . . . . . . 7
6. CBOR Mappings . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Privacy Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9.1. JSON Web Token Claims . . . . . . . . . . . . . . . . . . 9
9.2. CBOR Web Token Claims . . . . . . . . . . . . . . . . . . 9
9.3. OAuth Parameter Registration . . . . . . . . . . . . . . 9
9.4. OAuth Introspection Response Parameter Registration . . . 10
9.5. OAuth Parameters CBOR Mappings Registraton . . . . . . . 10
9.6. OAuth Token Introspection Response CBOR Mappings
Registration . . . . . . . . . . . . . . . . . . . . . . 11
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Overlap with OAuth work . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
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 may need to be updated to align them with ongoing OAuth
work. Therefore, these parameters and claims have been put into a
dedicated document, to facilitate their use and any potential updates
in a manner independent of [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].
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 CoAP [RFC7252]
definition, which is "An entity participating in the CoAP protocol"
is not used in this specification.
3. Parameters for the Token Endpoint
3.1. Client-to-AS Request
This document defines the following additional parameters for
requesting an access token from a token endpoint in the ACE framework
[I-D.ietf-ace-oauth-authz]:
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 reject a request
containing a symmetric key value in the 'req_cnf' field, since the
AS is expected to be able to generate better symmetric keys than a
constrained client. The AS MUST verify that the client really is
in possession of the corresponding key. Values of this parameter
follow the syntax of the "cnf" claim from section 3.1 of
[I-D.ietf-ace-cwt-proof-of-possession].
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 for better readability.
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Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: "application/ace+cbor"
Payload:
{
"req_cnf" : {
"COSE_Key" : {
"kty" : "EC",
"kid" : h'11',
"crv" : "P-256",
"x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
"y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
}
}
}
Figure 1: Example request for an access token bound to an asymmetric
key.
3.2. AS-to-Client Response
This document defines the following additional parameters for an AS
response to a request to the token endpoint:
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 of the
"cnf" claim from section 3.1 of
[I-D.ietf-ace-cwt-proof-of-possession]. 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 of the "cnf" claim from section 3.1 of
[I-D.ietf-ace-cwt-proof-of-possession]. 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.
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Header: Created (Code=2.01)
Content-Format: "application/ace+cbor"
Payload:
{
"access_token" : b64'SlAV32hkKG ...
(remainder of CWT omitted for brevity;
CWT contains COSE_Key in the "cnf" claim)',
"cnf" : {
"COSE_Key" : {
"kty" : "Symmetric",
"kid" : b64'39Gqlw',
"k" : b64'hJtXhkV8FJG+Onbc6mxCcQh'
}
}
}
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.
Header: Created (Code=2.01)
Content-Format: "application/ace+cbor"
Payload:
{
"access_token" : b64'0INDoQEKoQVNKkXfb7xaWqMTf6 ...
(remainder of CWT omitted for brevity;
CWT contains COSE_Key in the "cnf" claim)',
"rs_cnf" : {
"COSE_Key" : {
"kty" : "EC",
"kid" : h'12',
"crv" : "P-256",
"x" : b64'vO5+qsFi+R5vMw9XcSEeIguLVGyWWJsKxK0P0kx34fE',
"y" : b64'xkezjFXvu8TmLmUXIPAC1ddbLgwCzRMm5mK8oiK5BBY'
}
}
}
Figure 3: Example AS response, including the RS's public key.
3.3. The Resource Server Confirmation Claim
If the AS needs to convey a hint to the RS about which key it should
use to authenticate towards the client, this specification defines
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the "rs_cnf" claim, which MAY be used in the access token, with the
same syntax and semantics as defined in for the "rs_cnf" parameter.
4. Parameters for the Introspection Endpoint
4.1. AS-to-RS Response
This document defines the following additional parameters for an AS
response to a request to the introspection endpoint:
cnf
OPTIONAL. This field contains information about the proof-of-
possession key that binds the client to the access token. Values
of this parameter follow the syntax of the "cnf" claim from
section 3.1 of [I-D.ietf-ace-cwt-proof-of-possession]. See
Section 5 for additional discussion of the usage of this
parameter.
rs_cnf
OPTIONAL. If the RS uses asymmetric keys to authenticate towards
the client (e.g. with a DTLS-RPK handshake) and it has several
such keys (e.g. for different elliptic curves), the AS can give
the RS a hint using this parameter, as to which key it should use.
Values of this parameter follow the syntax of the "cnf" claim from
section 3.1 of [I-D.ietf-ace-cwt-proof-of-possession]. See
Section 5 for additional discussion of the usage of this
parameter.
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 and the "rs_cnf" parameter to indicate the key the RS is
supposed to use to authenticate to the client.
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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" : "EC",
"kid" : h'11',
"crv" : "P-256",
"x" : b64'usWxHK2PmfnHKwXPS54m0kTcGJ90UiglWiGahtagnv8',
"y" : b64'IBOL+C3BttVivg+lSreASjpkttcsz+1rb7btKLv8EX4'
}
},
"rs_cnf" : {
"COSE_Key" : {
"kty" : "EC",
"kid" : h'12',
"crv" : "P-256",
"x" : b64'vO5+qsFi+R5vMw9XcSEeIguLVGyWWJsKxK0P0kx34fE',
"y" : b64'xkezjFXvu8TmLmUXIPAC1ddbLgwCzRMm5mK8oiK5BBY'
}
}
}
Figure 4: Example introspection response.
5. Confirmation Method Parameters
The confirmation method parameters are used as follows:
o "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.
o "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.
o "cnf" in the introspection response AS -> RS, REQUIRED if the
access token that was subject to introspection is a proof-of-
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possession token, absent otherwise. Indicates the proof-of-
possession key bound to the access token.
o "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.
o "rs_cnf" in the introspection response AS -> RS, OPTIONAL,
contains the public key that the RS should use for authenticating
itself to the client (e.g. if the RS has several different public
keys, and there may be ambiguity as to which key to use).
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.
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 |
| rs_cnf | TBD (41) | map | introspection response |
| rs_cnf | TBD (41) | map | CWT claim |
\----------+----------+------------+------------------------/
Figure 5: CBOR mappings for new parameters and claims.
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7. Security Considerations
This document is an extension to [I-D.ietf-ace-oauth-authz]. All
security considerations from that document apply here as well.
8. Privacy Considerations
This document is an extension to [I-D.ietf-ace-oauth-authz]. All
privacy considerations from that document apply here as well.
9. IANA Considerations
9.1. JSON Web Token Claims
This specification registers the following new claim in the JSON Web
Token (JWT) registry of JSON Web Token Claims
[IANA.JsonWebTokenClaims]:
o Claim Name: "rs_cnf"
o Claim Description: public key used by RS to authenticate itself to
the client.
o Change Controller: IESG
o Reference: Section 3.3 of [this document]
9.2. CBOR Web Token Claims
This specification registers the following new claim in the "CBOR Web
Token (CWT) Claims" registry [IANA.CborWebTokenClaims].
o Claim Name: "rs_cnf"
o Claim Description: public key used by RS to authenticate itself to
the client.
o JWT Claim Name: rs_cnf
o Claim Key: TBD (suggested: 41)
o Claim Value Type(s): map
o Change Controller: IESG
o Specification Document(s): Section 3.3 of [this document]
9.3. OAuth Parameter Registration
This section registers the following parameters in the "OAuth
Parameters" registry [IANA.OAuthParameters]:
o Name: "req_cnf"
o Parameter Usage Location: token request
o Change Controller: IESG
o Reference: Section 5 of [this document]
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o Name: "rs_cnf"
o Parameter Usage Location: token response
o Change Controller: IESG
o Reference: Section 5 of [this document]
o Name: "cnf"
o Parameter Usage Location: token response
o Change Controller: IESG
o Reference: Section 5 of [this document]
9.4. OAuth Introspection Response Parameter Registration
This section registers the following parameters in the OAuth Token
Introspection Response registry [IANA.TokenIntrospectionResponse].
o Name: "cnf"
o Description: Key to prove the right to use a PoP token.
o Change Controller: IESG
o Reference: Section 4.1 of [this document]
o Name: "rs_cnf"
o Description: public key used by RS to authenticate itself to the
client.
o Change Controller: IESG
o Reference: Section 4.1 of [this document]
9.5. OAuth Parameters CBOR Mappings Registraton
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].
o Name: "req_cnf"
o CBOR key: TBD (suggested: 4)
o Change Controller: IESG
o Reference: Section 3.1 of [this document]
o Name: "cnf"
o CBOR key: TBD (suggested: 8)
o Change Controller: IESG
o Reference: Section 3.2 of [this document]
o Name: "rs_cnf"
o CBOR key: TBD (suggested: 41)
o Change Controller: IESG
o Reference: Section 3.2 of [this document]
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9.6. OAuth Token Introspection Response CBOR Mappings Registration
This section registers the following parameter mappings in the "OAuth
Token Introspection Response CBOR Mappings" registry established in
section 8.11. of [I-D.ietf-ace-oauth-authz].
o Name: "cnf"
o CBOR key: TBD (suggested: 8)
o Change Controller: IESG
o Reference: Section 4.1 of [this document]
o Name: "rs_cnf"
o CBOR key: TBD (suggested: 41)
o Change Controller: IESG
o Reference: Section 4.1 of [this document]
10. Acknowledgments
This document is a product of the ACE working group of the IETF.
Ludwig Seitz worked on this document as part of the CelticNext
projects CyberWI, and CRITISEC with funding from Vinnova.
11. References
11.1. Normative References
[I-D.ietf-ace-cwt-proof-of-possession]
Jones, M., Seitz, L., Selander, G., Erdtman, S., and H.
Tschofenig, "Proof-of-Possession Key Semantics for CBOR
Web Tokens (CWTs)", draft-ietf-ace-cwt-proof-of-
possession-11 (work in progress), October 2019.
[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)", draft-ietf-ace-oauth-authz-25
(work in progress), October 2019.
[IANA.CborWebTokenClaims]
IANA, "CBOR Web Token (CWT) Claims",
<https://www.iana.org/assignments/cwt/
cwt.xhtml#claims-registry>.
[IANA.JsonWebTokenClaims]
IANA, "JSON Web Token Claims",
<https://www.iana.org/assignments/jwt/jwt.xhtml#claims>.
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[IANA.OAuthParameters]
IANA, "OAuth Parameters",
<https://www.iana.org/assignments/oauth-parameters/
oauth-parameters.xhtml#parameters>.
[IANA.TokenIntrospectionResponse]
IANA, "OAuth Token Introspection Response",
<https://www.iana.org/assignments/oauth-parameters/
oauth-parameters.xhtml#token-introspection-response>.
[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>.
[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>.
[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>.
11.2. Informative References
[I-D.ietf-oauth-pop-key-distribution]
Bradley, J., Hunt, P., Jones, M., Tschofenig, H., and M.
Meszaros, "OAuth 2.0 Proof-of-Possession: Authorization
Server to Client Key Distribution", draft-ietf-oauth-pop-
key-distribution-07 (work in progress), March 2019.
[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>.
Appendix A. Overlap with OAuth work
This document overlaps with draft work from OAuth on proof-of-
possesion keys [I-D.ietf-oauth-pop-key-distribution].
The OAuth draft specifies the use of "req_cnf" and "cnf" for
requesting proof-of-possession tokens and indicating the key that the
AS has selected. It it was initially deemed that the work at OAuth
had been discontinued and therefore equivalent functionality was
defined here. Work in OAuth has since resumed, but it is lagging
behind the planned milestones of the ACE working group. We have
therefore split this work out into a separate document so that it can
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later be updated or obsoleted to align it with the final result of
the OAuth work, without affecting [I-D.ietf-ace-oauth-authz].
Author's Address
Ludwig Seitz
RISE
Scheelevaegen 17
Lund 223 70
Sweden
Email: ludwig.seitz@ri.se
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