<?xml version='1.0' encoding='utf-8'?>
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" version="3" category="std" consensus="true" docName="draft-ietf-ace-oauth-params-16" indexInclude="true" ipr="trust200902" number="9201" prepTime="2022-08-31T13:47:21" scripts="Common,Latin" sortRefs="true" submissionType="IETF" symRefs="true" tocDepth="4" tocInclude="true" xml:lang="en">
  <link href="https://datatracker.ietf.org/doc/draft-ietf-ace-oauth-params-16" rel="prev"/>
  <link href="https://dx.doi.org/10.17487/rfc9201" rel="alternate"/>
  <link href="urn:issn:2070-1721" rel="alternate"/>
  <front>
    <title abbrev="OAuth Parameters for ACE">Additional OAuth Parameters for Authentication and Authorization for Constrained Environments (ACE)</title>
    <seriesInfo name="RFC" value="9201" stream="IETF"/>
    <author fullname="Ludwig Seitz" initials="L." surname="Seitz">
      <organization showOnFrontPage="true">Combitech</organization>
      <address>
        <postal>
          <street>Djäknegatan 31</street>
          <code>211 35</code>
          <city>Malmö</city>
          <country>Sweden</country>
        </postal>
        <email>ludwig.seitz@combitech.com</email>
      </address>
    </author>
    <date month="08" year="2022"/>
    <area>Security</area>
    <workgroup>ACE</workgroup>
    <keyword>CoAP</keyword>
    <keyword>OAuth 2.0</keyword>
    <keyword>Access Control</keyword>
    <keyword>Authorization</keyword>
    <keyword>Internet of Things</keyword>
    <abstract pn="section-abstract">
      <t indent="0" pn="section-abstract-1">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 (PoP) key the client
      wishes to use, the PoP key that the authorization server
      has selected, and the PoP key the resource server uses to authenticate
      to the client.</t>
    </abstract>
    <boilerplate>
      <section anchor="status-of-memo" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.1">
        <name slugifiedName="name-status-of-this-memo">Status of This Memo</name>
        <t indent="0" pn="section-boilerplate.1-1">
            This is an Internet Standards Track document.
        </t>
        <t indent="0" pn="section-boilerplate.1-2">
            This document is a product of the Internet Engineering Task Force
            (IETF).  It represents the consensus of the IETF community.  It has
            received public review and has been approved for publication by
            the Internet Engineering Steering Group (IESG).  Further
            information on Internet Standards is available in Section 2 of 
            RFC 7841.
        </t>
        <t indent="0" pn="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <eref target="https://www.rfc-editor.org/info/rfc9201" brackets="none"/>.
        </t>
      </section>
      <section anchor="copyright" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.2">
        <name slugifiedName="name-copyright-notice">Copyright Notice</name>
        <t indent="0" pn="section-boilerplate.2-1">
            Copyright (c) 2022 IETF Trust and the persons identified as the
            document authors. All rights reserved.
        </t>
        <t indent="0" pn="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<eref target="https://trustee.ietf.org/license-info" brackets="none"/>) 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 extracted from this
            document must include Revised BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Revised BSD License.
        </t>
      </section>
    </boilerplate>
    <toc>
      <section anchor="toc" numbered="false" removeInRFC="false" toc="exclude" pn="section-toc.1">
        <name slugifiedName="name-table-of-contents">Table of Contents</name>
        <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1">
          <li pn="section-toc.1-1.1">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.1.1"><xref derivedContent="1" format="counter" sectionFormat="of" target="section-1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-introduction">Introduction</xref></t>
          </li>
          <li pn="section-toc.1-1.2">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.2.1"><xref derivedContent="2" format="counter" sectionFormat="of" target="section-2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-terminology">Terminology</xref></t>
          </li>
          <li pn="section-toc.1-1.3">
            <t indent="0" pn="section-toc.1-1.3.1"><xref derivedContent="3" format="counter" sectionFormat="of" target="section-3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-parameters-for-the-token-en">Parameters for the Token Endpoint</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.3.2">
              <li pn="section-toc.1-1.3.2.1">
                <t indent="0" keepWithNext="true" pn="section-toc.1-1.3.2.1.1"><xref derivedContent="3.1" format="counter" sectionFormat="of" target="section-3.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-client-to-as-request">Client-to-AS Request</xref></t>
              </li>
              <li pn="section-toc.1-1.3.2.2">
                <t indent="0" pn="section-toc.1-1.3.2.2.1"><xref derivedContent="3.2" format="counter" sectionFormat="of" target="section-3.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-as-to-client-response">AS-to-Client Response</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.4">
            <t indent="0" pn="section-toc.1-1.4.1"><xref derivedContent="4" format="counter" sectionFormat="of" target="section-4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-parameters-for-the-introspe">Parameters for the Introspection Endpoint</xref></t>
          </li>
          <li pn="section-toc.1-1.5">
            <t indent="0" pn="section-toc.1-1.5.1"><xref derivedContent="5" format="counter" sectionFormat="of" target="section-5"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-confirmation-method-paramet">Confirmation Method Parameters</xref></t>
          </li>
          <li pn="section-toc.1-1.6">
            <t indent="0" pn="section-toc.1-1.6.1"><xref derivedContent="6" format="counter" sectionFormat="of" target="section-6"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-cbor-mappings">CBOR Mappings</xref></t>
          </li>
          <li pn="section-toc.1-1.7">
            <t indent="0" pn="section-toc.1-1.7.1"><xref derivedContent="7" format="counter" sectionFormat="of" target="section-7"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-requirements-when-using-asy">Requirements When Using Asymmetric Keys</xref></t>
          </li>
          <li pn="section-toc.1-1.8">
            <t indent="0" pn="section-toc.1-1.8.1"><xref derivedContent="8" format="counter" sectionFormat="of" target="section-8"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-security-considerations">Security Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.9">
            <t indent="0" pn="section-toc.1-1.9.1"><xref derivedContent="9" format="counter" sectionFormat="of" target="section-9"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-privacy-considerations">Privacy Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.10">
            <t indent="0" pn="section-toc.1-1.10.1"><xref derivedContent="10" format="counter" sectionFormat="of" target="section-10"/>. <xref derivedContent="" format="title" sectionFormat="of" target="name-iana-considerations">IANA Considerations</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.10.2">
              <li pn="section-toc.1-1.10.2.1">
                <t indent="0" pn="section-toc.1-1.10.2.1.1"><xref derivedContent="10.1" format="counter" sectionFormat="of" target="section-10.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-oauth-parameter-registratio">OAuth Parameter Registration</xref></t>
              </li>
              <li pn="section-toc.1-1.10.2.2">
                <t indent="0" pn="section-toc.1-1.10.2.2.1"><xref derivedContent="10.2" format="counter" sectionFormat="of" target="section-10.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-oauth-parameters-cbor-mappi">OAuth Parameters CBOR Mappings Registration</xref></t>
              </li>
              <li pn="section-toc.1-1.10.2.3">
                <t indent="0" pn="section-toc.1-1.10.2.3.1"><xref derivedContent="10.3" format="counter" sectionFormat="of" target="section-10.3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-oauth-token-introspection-r">OAuth Token Introspection Response CBOR Mappings Registration</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.11">
            <t indent="0" pn="section-toc.1-1.11.1"><xref derivedContent="11" format="counter" sectionFormat="of" target="section-11"/>. <xref derivedContent="" format="title" sectionFormat="of" target="name-references">References</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.11.2">
              <li pn="section-toc.1-1.11.2.1">
                <t indent="0" pn="section-toc.1-1.11.2.1.1"><xref derivedContent="11.1" format="counter" sectionFormat="of" target="section-11.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-normative-references">Normative References</xref></t>
              </li>
              <li pn="section-toc.1-1.11.2.2">
                <t indent="0" pn="section-toc.1-1.11.2.2.1"><xref derivedContent="11.2" format="counter" sectionFormat="of" target="section-11.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-informative-references">Informative References</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.12">
            <t indent="0" pn="section-toc.1-1.12.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.a"/><xref derivedContent="" format="title" sectionFormat="of" target="name-acknowledgments">Acknowledgments</xref></t>
          </li>
          <li pn="section-toc.1-1.13">
            <t indent="0" pn="section-toc.1-1.13.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.b"/><xref derivedContent="" format="title" sectionFormat="of" target="name-authors-address">Author's Address</xref></t>
          </li>
        </ul>
      </section>
    </toc>
  </front>
  <middle>
    <section anchor="intro" numbered="true" toc="include" removeInRFC="false" pn="section-1">
      <name slugifiedName="name-introduction">Introduction</name>
      <t indent="0" pn="section-1-1">The Authentication and Authorization for Constrained Environments (ACE)
  specification <xref target="RFC9200" format="default" sectionFormat="of" derivedContent="RFC9200"/> requires some new
  parameters for interactions with the OAuth 2.0 <xref target="RFC6749" format="default" sectionFormat="of" derivedContent="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
  <xref target="RFC9200" format="default" sectionFormat="of" derivedContent="RFC9200"/>.</t>
      <t indent="0" pn="section-1-2">Note that although all examples are shown in Concise Binary Object
  Representation (CBOR) <xref target="RFC8949" format="default" sectionFormat="of" derivedContent="RFC8949"/>, JSON
  <xref target="RFC8259" format="default" sectionFormat="of" derivedContent="RFC8259"/> <bcp14>MAY</bcp14> be used as an alternative for HTTP-based
  communications, as specified in <xref target="RFC9200" format="default" sectionFormat="of" derivedContent="RFC9200"/>.</t>
    </section>
    <section anchor="terminology" numbered="true" toc="include" removeInRFC="false" pn="section-2">
      <name slugifiedName="name-terminology">Terminology</name>
      <t indent="0" pn="section-2-1">The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and
"<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as described in BCP 14 <xref target="RFC2119" format="default" sectionFormat="of" derivedContent="RFC2119"/> <xref target="RFC8174" format="default" sectionFormat="of" derivedContent="RFC8174"/> when, and only when, they appear in all capitals, as shown here.</t>
      <t indent="0" pn="section-2-2">Readers are assumed to be familiar with the terminology from <xref target="RFC9200" format="default" sectionFormat="of" derivedContent="RFC9200"/>, especially the terminology
  for entities in the architecture such as client (C), resource server (RS),
  and authorization server (AS).</t>
      <t indent="0" pn="section-2-3">Terminology from <xref target="RFC8152" format="default" sectionFormat="of" derivedContent="RFC8152"/> is used in the examples,
  especially COSE_Key, which is defined in <xref target="RFC8152" sectionFormat="of" section="7" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8152#section-7" derivedContent="RFC8152"/>.</t>
      <t indent="0" pn="section-2-4">Note that the term "endpoint" is used here following its OAuth 2.0
      <xref target="RFC6749" format="default" sectionFormat="of" derivedContent="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) <xref target="RFC7252" format="default" sectionFormat="of" derivedContent="RFC7252"/> definition,
      which is "[a]n entity participating in the CoAP protocol", is not used in this
      specification.</t>
    </section>
    <section anchor="tokenEndpoint" numbered="true" toc="include" removeInRFC="false" pn="section-3">
      <name slugifiedName="name-parameters-for-the-token-en">Parameters for the Token Endpoint</name>
      <t indent="0" pn="section-3-1">This section defines additional parameters for the interactions with
  the token endpoint in the ACE framework <xref target="RFC9200" format="default" sectionFormat="of" derivedContent="RFC9200"/>.</t>
      <section anchor="tokenRequest" numbered="true" toc="include" removeInRFC="false" pn="section-3.1">
        <name slugifiedName="name-client-to-as-request">Client-to-AS Request</name>
        <t indent="0" pn="section-3.1-1">This section defines the <tt>req_cnf</tt> parameter allowing clients to
   request a specific PoP key in an access token from a token
   endpoint in the ACE framework <xref target="RFC9200" format="default" sectionFormat="of" derivedContent="RFC9200"/>:
 
        </t>
        <dl newline="true" spacing="normal" indent="3" pn="section-3.1-2">
          <dt pn="section-3.1-2.1">req_cnf</dt>
          <dd pn="section-3.1-2.2">
            <bcp14>OPTIONAL</bcp14>.  This field contains information about the key the
	client would like to bind to the access token for proof of possession.
	It is <bcp14>RECOMMENDED</bcp14> that an AS rejects a request containing a symmetric
	key value in the <tt>req_cnf</tt> 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 <bcp14>MUST</bcp14> verify that the client
	really is in possession of the corresponding key.  Profiles of
	<xref target="RFC9200" format="default" sectionFormat="of" derivedContent="RFC9200"/> using this specification
	<bcp14>MUST</bcp14>
	define the PoP 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 <tt>cnf</tt> claim either from
	<xref target="RFC8747" sectionFormat="of" section="3.1" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8747#section-3.1" derivedContent="RFC8747"/> for CBOR-based
	interactions or from
	<xref target="RFC7800" sectionFormat="of" section="3.1" format="default" derivedLink="https://rfc-editor.org/rfc/rfc7800#section-3.1" derivedContent="RFC7800"/> for JSON-based
	  interactions.</dd>
        </dl>
        <t indent="0" pn="section-3.1-3"><xref target="fig_symmATreq" format="default" sectionFormat="of" derivedContent="Figure 1"/> shows a request for an access
	token using the <tt>req_cnf</tt> parameter to request a specific public key as a
	PoP key.  The content is displayed in CBOR diagnostic
	notation with line breaks for better readability.</t>
        <figure anchor="fig_symmATreq" align="left" suppress-title="false" pn="figure-1">
          <name slugifiedName="name-example-request-for-an-acce">Example Request for an Access Token Bound to an Asymmetric Key</name>
          <sourcecode name="" type="cbor-diag" markers="false" pn="section-3.1-4.1">
Header: POST (Code=0.02)
Uri-Host: "as.example.com"
Uri-Path: "token"
Content-Format: application/ace+cbor
Payload:
{
   / req_cnf / 4 : {
     / COSE_Key / 1 : {
     / kty /  1 : 2 /EC2/,
     / kid /  2 : h'11',
     / crv / -1 : 1 /P-256/,
     / x /   -2 : h'BAC5B11CAD8F99F9C72B05CF4B9E26D24
                  4DC189F745228255A219A86D6A09EFF',
     / y /   -3 : h'20138BF82DC1B6D562BE0FA54AB7804A3
                  A64B6D72CCFED6B6FB6ED28BBFC117E'
      }
   }
 }
</sourcecode>
        </figure>
      </section>
      <section anchor="tokenResponse" numbered="true" toc="include" removeInRFC="false" pn="section-3.2">
        <name slugifiedName="name-as-to-client-response">AS-to-Client Response</name>
        <t indent="0" pn="section-3.2-1">This section defines the following additional parameters for
    an AS response to a request to the token endpoint:

        </t>
        <dl newline="true" spacing="normal" indent="3" pn="section-3.2-2">
          <dt pn="section-3.2-2.1">cnf</dt>
          <dd pn="section-3.2-2.2">
            <bcp14>REQUIRED</bcp14> if the token type is "pop" and a symmetric key is used.
	<bcp14>MAY</bcp14> be present for asymmetric PoP keys.  This field
	contains the PoP key that the AS selected for the
	token. 	Values of this parameter follow the syntax and semantics of the
	<tt>cnf</tt> claim either from <xref target="RFC8747" sectionFormat="of" section="3.1" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8747#section-3.1" derivedContent="RFC8747"/>
	for
	CBOR-based interactions or from <xref target="RFC7800" sectionFormat="of" section="3.1" format="default" derivedLink="https://rfc-editor.org/rfc/rfc7800#section-3.1" derivedContent="RFC7800"/>
	for JSON-based interactions.  See <xref target="paramCnf" format="default" sectionFormat="of" derivedContent="Section 5"/> for
	additional discussion of the usage of this parameter.
          </dd>
          <dt pn="section-3.2-2.3">rs_cnf</dt>
          <dd pn="section-3.2-2.4">
            <bcp14>OPTIONAL</bcp14> if the token type is "pop" and asymmetric keys are used.
	<bcp14>MUST NOT</bcp14> 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 <tt>cnf</tt> claim either from
	<xref target="RFC8747" sectionFormat="of" section="3.1" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8747#section-3.1" derivedContent="RFC8747"/> for CBOR-based
	interactions or from
	<xref target="RFC7800" sectionFormat="of" section="3.1" format="default" derivedLink="https://rfc-editor.org/rfc/rfc7800#section-3.1" derivedContent="RFC7800"/> for JSON-based
	interactions.  See
	<xref target="paramCnf" format="default" sectionFormat="of" derivedContent="Section 5"/> for additional discussion of the usage
	of this	parameter. </dd>
        </dl>
        <t indent="0" pn="section-3.2-3"><xref target="fig_symmATres" format="default" sectionFormat="of" derivedContent="Figure 2"/> shows an AS response containing
	a token and a <tt>cnf</tt> parameter with a symmetric PoP key.</t>
        <figure anchor="fig_symmATres" align="left" suppress-title="false" pn="figure-2">
          <name slugifiedName="name-example-as-response-with-an">Example AS Response with an Access Token Bound to a Symmetric Key</name>
          <sourcecode name="" type="cbor-diag" markers="false" pn="section-3.2-4.1">
Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Payload:
{
  / access_token / 1 : h'4A5015DF686428/...
   (remainder of CWT omitted for brevity;
   CWT contains COSE_Key in the "cnf" claim)/',
  / cnf / 8 : {
   / COSE_Key / 1 : {
      / kty / 1 : 4 / Symmetric /,
      / kid / 2 : h'DFD1AA97',
      / k /  -1 : h'849B5786457C1491BE3A76DCEA6C427108'
    }
  }
}
</sourcecode>
        </figure>
        <t indent="0" pn="section-3.2-5"><xref target="fig_asymmATres" format="default" sectionFormat="of" derivedContent="Figure 3"/> shows an AS response containing
	a token bound to a previously requested asymmetric PoP key (not
	shown) and an <tt>rs_cnf</tt> parameter containing the public key of the RS.</t>
        <figure anchor="fig_asymmATres" align="left" suppress-title="false" pn="figure-3">
          <name slugifiedName="name-example-as-response-includi">Example AS Response Including the RS's Public Key</name>
          <sourcecode name="" type="cbor-diag" markers="false" pn="section-3.2-6.1">
Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Payload:
{
  / access_token / 1 : h'D08343A1010AA1054D2A45DF6FBC5A5A/...
   (remainder of CWT omitted for brevity)/',
  / rs_cnf / 41 : {
    / COSE_Key / 1 : {
     / kty /  1 : 2 /EC2/,
     / kid /  2 : h'12',
     / crv / -1 : 1 /P-256/,
      / x /  -2 : h'BCEE7EAAC162F91E6F330F5771211E220
                  B8B546C96589B0AC4AD0FD24C77E1F1',
      / y /  -3 : h'C647B38C55EFBBC4E62E651720F002D5D
                  75B2E0C02CD1326E662BCA222B90416'
    }
  }
}
</sourcecode>
        </figure>
      </section>
    </section>
    <section anchor="introsp" numbered="true" toc="include" removeInRFC="false" pn="section-4">
      <name slugifiedName="name-parameters-for-the-introspe">Parameters for the Introspection Endpoint</name>
      <t indent="0" pn="section-4-1">This section defines the use of CBOR instead of JSON for the <tt>cnf</tt>
      introspection response parameter specified in <xref target="RFC8705" sectionFormat="of" section="9.4" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8705#section-9.4" derivedContent="RFC8705"/>.</t>
      <t indent="0" pn="section-4-2">If CBOR is used instead of JSON in an interaction with the introspection
      endpoint, the AS <bcp14>MUST</bcp14> use the parameter mapping specified in <xref target="fig_cborParameters" format="default" sectionFormat="of" derivedContent="Table 1"/> and the value must follow the syntax
      of <tt>cnf</tt> claim values from <xref target="RFC8747" sectionFormat="of" section="3.1" format="default" derivedLink="https://rfc-editor.org/rfc/rfc8747#section-3.1" derivedContent="RFC8747"/>.</t>
      <t indent="0" pn="section-4-3"><xref target="fig_introRes" format="default" sectionFormat="of" derivedContent="Figure 4"/> shows an AS response to an introspection
  request including the <tt>cnf</tt> parameter to indicate the PoP key bound to the token.</t>
      <figure anchor="fig_introRes" align="left" suppress-title="false" pn="figure-4">
        <name slugifiedName="name-example-introspection-respo">Example Introspection Response</name>
        <sourcecode name="" type="cbor-diag" markers="false" pn="section-4-4.1">
Header: Created (Code=2.01)
Content-Format: application/ace+cbor
Payload:
{
  / active / 10 : true,
  / scope / 9 : "read",
  / aud / 3 : "tempSensor4711",
  / cnf / 8 : {
    / COSE_Key / 1 : {
      / kty /  1 : 2 /EC2/,
      / kid /  2 : h'11',
      / crv / -1 : 1 /P-256/,
      / x /   -2 : h'BAC5B11CAD8F99F9C72B05CF4B9E26D24
                   4DC189F745228255A219A86D6A09EFF',
      / y /   -3 : h'20138BF82DC1B6D562BE0FA54AB7804A3
                   A64B6D72CCFED6B6FB6ED28BBFC117E'
    }
  }
}
</sourcecode>
      </figure>
    </section>
    <section anchor="paramCnf" numbered="true" toc="include" removeInRFC="false" pn="section-5">
      <name slugifiedName="name-confirmation-method-paramet">Confirmation Method Parameters</name>
      <t indent="0" pn="section-5-1">The confirmation method parameters are used in
  <xref target="RFC9200" format="default" sectionFormat="of" derivedContent="RFC9200"/> as follows:
      </t>
      <ul spacing="normal" bare="false" empty="false" indent="3" pn="section-5-2">
        <li pn="section-5-2.1">
          <tt>req_cnf</tt> in the access token request C -&gt; AS, <bcp14>OPTIONAL</bcp14> to
	indicate the  client's raw public key or the key identifier of a previously
	established key between the C and RS that the client wishes to use
	for proof of possession of the access token.</li>
        <li pn="section-5-2.2">
          <tt>cnf</tt> in the token response AS -&gt; C, <bcp14>OPTIONAL</bcp14> if using an
	asymmetric key or a key that the client requested via a key identifier
	in the request. <bcp14>REQUIRED</bcp14> if the client didn't specify a <tt>req_cnf</tt> and
	symmetric keys are used.  Used to indicate the symmetric key generated
	by the AS for proof of possession of the access token.</li>
        <li pn="section-5-2.3">
          <tt>cnf</tt> in the introspection response AS -&gt; RS, <bcp14>REQUIRED</bcp14> if the
	access token that was subject to introspection is a PoP
	token, absent otherwise.  Indicates the PoP key bound
	to the access token.</li>
        <li pn="section-5-2.4">
          <tt>rs_cnf</tt> in the token response AS -&gt; C, <bcp14>OPTIONAL</bcp14> to indicate
	the public key of the RS if it uses one to authenticate itself to the client
	and the binding between the key and RS identity is not established through
	other means.</li>
      </ul>
      <t indent="0" pn="section-5-3">Note that the COSE_Key structure in a confirmation claim or parameter
      may contain an <tt>alg</tt> or <tt>key_ops</tt> parameter.  If such parameters are
      present, a client <bcp14>MUST NOT</bcp14> use a key that is incompatible with
      the profile or PoP algorithm according to those
      parameters. An RS <bcp14>MUST</bcp14> reject a proof of possession using such a key
      with a response code equivalent to the CoAP code 4.00 (Bad Request).
      </t>
      <t indent="0" pn="section-5-4">If an access token is issued for an audience that includes several RSs,
  the <tt>rs_cnf</tt> parameter <bcp14>MUST NOT</bcp14> 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.</t>
    </section>
    <section anchor="paramsCbor" numbered="true" toc="include" removeInRFC="false" pn="section-6">
      <name slugifiedName="name-cbor-mappings">CBOR Mappings</name>
      <t indent="0" pn="section-6-1">If CBOR is used, the new parameters and claims defined in this document
  <bcp14>MUST</bcp14> be mapped to CBOR types, as specified in <xref target="fig_cborParameters" format="default" sectionFormat="of" derivedContent="Table 1"/>, using the given integer abbreviation for the
  map key.</t>
      <table anchor="fig_cborParameters" align="left" pn="table-1">
        <name slugifiedName="name-cbor-mappings-for-new-param">CBOR Mappings for New Parameters and Claims</name>
        <thead>
          <tr>
            <th align="left" colspan="1" rowspan="1">Name</th>
            <th align="left" colspan="1" rowspan="1">CBOR Key</th>
            <th align="left" colspan="1" rowspan="1">Value Type</th>
            <th align="left" colspan="1" rowspan="1">Usage</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td align="left" colspan="1" rowspan="1">req_cnf</td>
            <td align="left" colspan="1" rowspan="1">4</td>
            <td align="left" colspan="1" rowspan="1">map</td>
            <td align="left" colspan="1" rowspan="1">token request</td>
          </tr>
          <tr>
            <td align="left" colspan="1" rowspan="1">cnf</td>
            <td align="left" colspan="1" rowspan="1">8</td>
            <td align="left" colspan="1" rowspan="1">map</td>
            <td align="left" colspan="1" rowspan="1">token response</td>
          </tr>
          <tr>
            <td align="left" colspan="1" rowspan="1">cnf</td>
            <td align="left" colspan="1" rowspan="1">8</td>
            <td align="left" colspan="1" rowspan="1">map</td>
            <td align="left" colspan="1" rowspan="1">introspection response</td>
          </tr>
          <tr>
            <td align="left" colspan="1" rowspan="1">rs_cnf</td>
            <td align="left" colspan="1" rowspan="1">41</td>
            <td align="left" colspan="1" rowspan="1">map</td>
            <td align="left" colspan="1" rowspan="1">token response</td>
          </tr>
        </tbody>
      </table>
    </section>
    <section anchor="asymmReq" numbered="true" toc="include" removeInRFC="false" pn="section-7">
      <name slugifiedName="name-requirements-when-using-asy">Requirements When Using Asymmetric Keys</name>
      <t indent="0" pn="section-7-1">An RS using asymmetric keys to authenticate to the client <bcp14>MUST NOT</bcp14>
      hold several different asymmetric key pairs applicable to the same
      authentication algorithm.  For example, when using DTLS, the RS <bcp14>MUST NOT</bcp14> 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.</t>
    </section>
    <section anchor="security" numbered="true" toc="include" removeInRFC="false" pn="section-8">
      <name slugifiedName="name-security-considerations">Security Considerations</name>
      <t indent="0" pn="section-8-1">This document is an extension to <xref target="RFC9200" format="default" sectionFormat="of" derivedContent="RFC9200"/>. All
      security considerations from that document apply here as well.</t>
    </section>
    <section anchor="privacy" numbered="true" toc="include" removeInRFC="false" pn="section-9">
      <name slugifiedName="name-privacy-considerations">Privacy Considerations</name>
      <t indent="0" pn="section-9-1">This document is an extension to <xref target="RFC9200" format="default" sectionFormat="of" derivedContent="RFC9200"/>. All
      privacy considerations from that document apply here as well.</t>
    </section>
    <section anchor="iana" numbered="true" toc="include" removeInRFC="false" pn="section-10">
      <name slugifiedName="name-iana-considerations">IANA Considerations</name>
      <section anchor="IANAOAuthParameter" numbered="true" toc="include" removeInRFC="false" pn="section-10.1">
        <name slugifiedName="name-oauth-parameter-registratio">OAuth Parameter Registration</name>
        <t indent="0" pn="section-10.1-1">This section registers the following parameters in the "OAuth
	Parameters" registry <xref target="IANA.OAuthParameters" format="default" sectionFormat="of" derivedContent="IANA.OAuthParameters"/>:</t>
        <dl newline="false" spacing="compact" indent="3" pn="section-10.1-2">
          <dt pn="section-10.1-2.1">Name:</dt>
          <dd pn="section-10.1-2.2">
            <tt>req_cnf</tt></dd>
          <dt pn="section-10.1-2.3">Parameter Usage Location:</dt>
          <dd pn="section-10.1-2.4">token request</dd>
          <dt pn="section-10.1-2.5">Change Controller:</dt>
          <dd pn="section-10.1-2.6">IETF</dd>
          <dt pn="section-10.1-2.7">Reference:</dt>
          <dd pn="section-10.1-2.8">
            <xref target="paramCnf" format="default" sectionFormat="of" derivedContent="Section 5"/> of RFC 9201</dd>
        </dl>
        <dl newline="false" spacing="compact" indent="3" pn="section-10.1-3">
          <dt pn="section-10.1-3.1">Name:</dt>
          <dd pn="section-10.1-3.2">
            <tt>rs_cnf</tt></dd>
          <dt pn="section-10.1-3.3">Parameter Usage Location:</dt>
          <dd pn="section-10.1-3.4">token response</dd>
          <dt pn="section-10.1-3.5">Change Controller:</dt>
          <dd pn="section-10.1-3.6">IETF</dd>
          <dt pn="section-10.1-3.7">Reference:</dt>
          <dd pn="section-10.1-3.8">
            <xref target="paramCnf" format="default" sectionFormat="of" derivedContent="Section 5"/> of RFC 9201</dd>
        </dl>
        <dl newline="false" spacing="compact" indent="3" pn="section-10.1-4">
          <dt pn="section-10.1-4.1">Name:</dt>
          <dd pn="section-10.1-4.2">
            <tt>cnf</tt></dd>
          <dt pn="section-10.1-4.3">Parameter Usage Location:</dt>
          <dd pn="section-10.1-4.4">token response</dd>
          <dt pn="section-10.1-4.5">Change Controller:</dt>
          <dd pn="section-10.1-4.6">IETF</dd>
          <dt pn="section-10.1-4.7">Reference:</dt>
          <dd pn="section-10.1-4.8">
            <xref target="paramCnf" format="default" sectionFormat="of" derivedContent="Section 5"/> of RFC 9201</dd>
        </dl>
      </section>
      <section anchor="IANATokenCBORMappingRegistration" numbered="true" toc="include" removeInRFC="false" pn="section-10.2">
        <name slugifiedName="name-oauth-parameters-cbor-mappi">OAuth Parameters CBOR Mappings Registration</name>
        <t indent="0" pn="section-10.2-1">This section registers the following parameter mappings
	in the "OAuth Parameters CBOR Mappings" registry established in
	<xref target="RFC9200" sectionFormat="of" section="8.10" format="default" derivedLink="https://rfc-editor.org/rfc/rfc9200#section-8.10" derivedContent="RFC9200"/>.</t>
        <dl newline="false" spacing="compact" indent="3" pn="section-10.2-2">
          <dt pn="section-10.2-2.1">Name:</dt>
          <dd pn="section-10.2-2.2">
            <tt>req_cnf</tt></dd>
          <dt pn="section-10.2-2.3">CBOR Key:</dt>
          <dd pn="section-10.2-2.4">4</dd>
          <dt pn="section-10.2-2.5">Value Type:</dt>
          <dd pn="section-10.2-2.6">map</dd>
          <dt pn="section-10.2-2.7">Reference:</dt>
          <dd pn="section-10.2-2.8">
            <xref target="tokenRequest" format="default" sectionFormat="of" derivedContent="Section 3.1"/> of RFC 9201</dd>
          <dt pn="section-10.2-2.9">Original Specification:</dt>
          <dd pn="section-10.2-2.10">RFC 9201</dd>
        </dl>
        <dl newline="false" spacing="compact" indent="3" pn="section-10.2-3">
          <dt pn="section-10.2-3.1">Name:</dt>
          <dd pn="section-10.2-3.2">
            <tt>cnf</tt></dd>
          <dt pn="section-10.2-3.3">CBOR Key:</dt>
          <dd pn="section-10.2-3.4">8</dd>
          <dt pn="section-10.2-3.5">Value Type:</dt>
          <dd pn="section-10.2-3.6">map</dd>
          <dt pn="section-10.2-3.7">Reference:</dt>
          <dd pn="section-10.2-3.8">
            <xref target="tokenResponse" format="default" sectionFormat="of" derivedContent="Section 3.2"/> of RFC 9201</dd>
          <dt pn="section-10.2-3.9">Original Specification:</dt>
          <dd pn="section-10.2-3.10">RFC 9201</dd>
        </dl>
        <dl newline="false" spacing="compact" indent="3" pn="section-10.2-4">
          <dt pn="section-10.2-4.1">Name:</dt>
          <dd pn="section-10.2-4.2">
            <tt>rs_cnf</tt></dd>
          <dt pn="section-10.2-4.3">CBOR Key:</dt>
          <dd pn="section-10.2-4.4">41</dd>
          <dt pn="section-10.2-4.5">Value Type:</dt>
          <dd pn="section-10.2-4.6">map</dd>
          <dt pn="section-10.2-4.7">Reference:</dt>
          <dd pn="section-10.2-4.8">
            <xref target="tokenResponse" format="default" sectionFormat="of" derivedContent="Section 3.2"/> of RFC 9201</dd>
          <dt pn="section-10.2-4.9">Original Specification:</dt>
          <dd pn="section-10.2-4.10">RFC 9201</dd>
        </dl>
      </section>
      <section anchor="IANAIntrospectCBORMappingRegistration" numbered="true" toc="include" removeInRFC="false" pn="section-10.3">
        <name slugifiedName="name-oauth-token-introspection-r">OAuth Token Introspection Response CBOR Mappings Registration</name>
        <t indent="0" pn="section-10.3-1">This section registers the following parameter mapping
	in the "OAuth Token Introspection Response CBOR Mappings" registry
	established in <xref target="RFC9200" sectionFormat="of" section="8.12" format="default" derivedLink="https://rfc-editor.org/rfc/rfc9200#section-8.12" derivedContent="RFC9200"/>.</t>
        <dl newline="false" spacing="compact" indent="3" pn="section-10.3-2">
          <dt pn="section-10.3-2.1">Name:</dt>
          <dd pn="section-10.3-2.2">
            <tt>cnf</tt></dd>
          <dt pn="section-10.3-2.3">CBOR Key:</dt>
          <dd pn="section-10.3-2.4">8</dd>
          <dt pn="section-10.3-2.5">Value Type:</dt>
          <dd pn="section-10.3-2.6">map</dd>
          <dt pn="section-10.3-2.7">Reference:</dt>
          <dd pn="section-10.3-2.8">
            <xref target="introsp" format="default" sectionFormat="of" derivedContent="Section 4"/> of RFC 9201</dd>
          <dt pn="section-10.3-2.9">Original Specification:</dt>
          <dd pn="section-10.3-2.10">
            <xref target="RFC8705" format="default" sectionFormat="of" derivedContent="RFC8705"/></dd>
        </dl>
      </section>
    </section>
  </middle>
  <back>
    <references pn="section-11">
      <name slugifiedName="name-references">References</name>
      <references pn="section-11.1">
        <name slugifiedName="name-normative-references">Normative References</name>
        <reference anchor="IANA.OAuthParameters" target="https://www.iana.org/assignments/oauth-parameters" quoteTitle="true" derivedAnchor="IANA.OAuthParameters">
          <front>
            <title>OAuth Parameters</title>
            <author>
              <organization showOnFrontPage="true">IANA</organization>
            </author>
          </front>
        </reference>
        <reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2119" quoteTitle="true" derivedAnchor="RFC2119">
          <front>
            <title>Key words for use in RFCs to Indicate Requirement Levels</title>
            <author fullname="S. Bradner" initials="S." surname="Bradner"/>
            <date month="March" year="1997"/>
            <abstract>
              <t indent="0">In many standards track documents several words are used to signify the requirements in the specification.  These words are often capitalized.  This document defines these words as they should be interpreted in IETF documents.  This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="2119"/>
          <seriesInfo name="DOI" value="10.17487/RFC2119"/>
        </reference>
        <reference anchor="RFC6749" target="https://www.rfc-editor.org/info/rfc6749" quoteTitle="true" derivedAnchor="RFC6749">
          <front>
            <title>The OAuth 2.0 Authorization Framework</title>
            <author fullname="D. Hardt" initials="D." role="editor" surname="Hardt"/>
            <date month="October" year="2012"/>
            <abstract>
              <t indent="0">The OAuth 2.0 authorization framework enables a third-party application to obtain limited access to an HTTP service, either on behalf of a resource owner by orchestrating an approval interaction between the resource owner and the HTTP service, or by allowing the third-party application to obtain access on its own behalf.  This specification replaces and obsoletes the OAuth 1.0 protocol described in RFC 5849. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="6749"/>
          <seriesInfo name="DOI" value="10.17487/RFC6749"/>
        </reference>
        <reference anchor="RFC7800" target="https://www.rfc-editor.org/info/rfc7800" quoteTitle="true" derivedAnchor="RFC7800">
          <front>
            <title>Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)</title>
            <author fullname="M. Jones" initials="M." surname="Jones"/>
            <author fullname="J. Bradley" initials="J." surname="Bradley"/>
            <author fullname="H. Tschofenig" initials="H." surname="Tschofenig"/>
            <date month="April" year="2016"/>
            <abstract>
              <t indent="0">This specification describes how to declare in a JSON Web Token (JWT) that the presenter of the JWT possesses a particular proof-of- possession key and how the recipient can cryptographically confirm proof of possession of the key by the presenter.  Being able to prove possession of a key is also sometimes described as the presenter being a holder-of-key.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7800"/>
          <seriesInfo name="DOI" value="10.17487/RFC7800"/>
        </reference>
        <reference anchor="RFC8152" target="https://www.rfc-editor.org/info/rfc8152" quoteTitle="true" derivedAnchor="RFC8152">
          <front>
            <title>CBOR Object Signing and Encryption (COSE)</title>
            <author fullname="J. Schaad" initials="J." surname="Schaad"/>
            <date month="July" year="2017"/>
            <abstract>
              <t indent="0">Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size.  There is a need for the ability to have basic security services defined for this data format.  This document defines the CBOR Object Signing and Encryption (COSE) protocol.  This specification describes how to create and process signatures, message authentication codes, and encryption using CBOR for serialization.  This specification additionally describes how to represent cryptographic keys using CBOR.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8152"/>
          <seriesInfo name="DOI" value="10.17487/RFC8152"/>
        </reference>
        <reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8174" quoteTitle="true" derivedAnchor="RFC8174">
          <front>
            <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
            <author fullname="B. Leiba" initials="B." surname="Leiba"/>
            <date month="May" year="2017"/>
            <abstract>
              <t indent="0">RFC 2119 specifies common key words that may be used in protocol specifications.  This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="8174"/>
          <seriesInfo name="DOI" value="10.17487/RFC8174"/>
        </reference>
        <reference anchor="RFC8259" target="https://www.rfc-editor.org/info/rfc8259" quoteTitle="true" derivedAnchor="RFC8259">
          <front>
            <title>The JavaScript Object Notation (JSON) Data Interchange Format</title>
            <author fullname="T. Bray" initials="T." role="editor" surname="Bray"/>
            <date month="December" year="2017"/>
            <abstract>
              <t indent="0">JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.</t>
              <t indent="0">This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance.</t>
            </abstract>
          </front>
          <seriesInfo name="STD" value="90"/>
          <seriesInfo name="RFC" value="8259"/>
          <seriesInfo name="DOI" value="10.17487/RFC8259"/>
        </reference>
        <reference anchor="RFC8705" target="https://www.rfc-editor.org/info/rfc8705" quoteTitle="true" derivedAnchor="RFC8705">
          <front>
            <title>OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens</title>
            <author fullname="B. Campbell" initials="B." surname="Campbell"/>
            <author fullname="J. Bradley" initials="J." surname="Bradley"/>
            <author fullname="N. Sakimura" initials="N." surname="Sakimura"/>
            <author fullname="T. Lodderstedt" initials="T." surname="Lodderstedt"/>
            <date month="February" year="2020"/>
            <abstract>
              <t indent="0">This document describes OAuth client authentication and certificate-bound access and refresh tokens using mutual Transport Layer Security (TLS) authentication with X.509 certificates.  OAuth clients are provided a mechanism for authentication to the authorization server using mutual TLS, based on either self-signed certificates or public key infrastructure (PKI).  OAuth authorization servers are provided a mechanism for binding access tokens to a client's mutual-TLS certificate, and OAuth protected resources are provided a method for ensuring that such an access token presented to it was issued to the client presenting the token.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8705"/>
          <seriesInfo name="DOI" value="10.17487/RFC8705"/>
        </reference>
        <reference anchor="RFC8747" target="https://www.rfc-editor.org/info/rfc8747" quoteTitle="true" derivedAnchor="RFC8747">
          <front>
            <title>Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs)</title>
            <author fullname="M. Jones" initials="M." surname="Jones"/>
            <author fullname="L. Seitz" initials="L." surname="Seitz"/>
            <author fullname="G. Selander" initials="G." surname="Selander"/>
            <author fullname="S. Erdtman" initials="S." surname="Erdtman"/>
            <author fullname="H. Tschofenig" initials="H." surname="Tschofenig"/>
            <date month="March" year="2020"/>
            <abstract>
              <t indent="0">This specification describes how to declare in a CBOR Web Token (CWT) (which is defined by RFC 8392) that the presenter of the CWT possesses a particular proof-of-possession key.  Being able to prove possession of a key is also sometimes described as being the holder-of-key.  This specification provides equivalent functionality to "Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)" (RFC 7800) but using Concise Binary Object Representation (CBOR) and CWTs rather than JavaScript Object Notation (JSON) and JSON Web Tokens (JWTs).</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8747"/>
          <seriesInfo name="DOI" value="10.17487/RFC8747"/>
        </reference>
        <reference anchor="RFC8949" target="https://www.rfc-editor.org/info/rfc8949" quoteTitle="true" derivedAnchor="RFC8949">
          <front>
            <title>Concise Binary Object Representation (CBOR)</title>
            <author fullname="C. Bormann" initials="C." surname="Bormann"/>
            <author fullname="P. Hoffman" initials="P." surname="Hoffman"/>
            <date month="December" year="2020"/>
            <abstract>
              <t indent="0">The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack.</t>
              <t indent="0">This document obsoletes RFC 7049, providing editorial improvements, new details, and errata fixes while keeping full compatibility with the interchange format of RFC 7049. It does not create a new version of the format.</t>
            </abstract>
          </front>
          <seriesInfo name="STD" value="94"/>
          <seriesInfo name="RFC" value="8949"/>
          <seriesInfo name="DOI" value="10.17487/RFC8949"/>
        </reference>
        <reference anchor="RFC9200" target="https://www.rfc-editor.org/info/rfc9200" quoteTitle="true" derivedAnchor="RFC9200">
          <front>
            <title>Authentication and Authorization for Constrained Environments (ACE) Using the OAuth 2.0 Framework (ACE-OAuth)</title>
            <author initials="L" surname="Seitz" fullname="Ludwig Seitz">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="G" surname="Selander" fullname="Göran Selander">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="E" surname="Wahlstroem" fullname="Erik Wahlstroem">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="S" surname="Erdtman" fullname="Samuel Erdtman">
              <organization showOnFrontPage="true"/>
            </author>
            <author initials="H" surname="Tschofenig" fullname="Hannes Tschofenig">
              <organization showOnFrontPage="true"/>
            </author>
            <date year="2022" month="August"/>
          </front>
          <seriesInfo name="RFC" value="9200"/>
          <seriesInfo name="DOI" value="10.17487/RFC9200"/>
        </reference>
      </references>
      <references pn="section-11.2">
        <name slugifiedName="name-informative-references">Informative References</name>
        <reference anchor="RFC7252" target="https://www.rfc-editor.org/info/rfc7252" quoteTitle="true" derivedAnchor="RFC7252">
          <front>
            <title>The Constrained Application Protocol (CoAP)</title>
            <author fullname="Z. Shelby" initials="Z." surname="Shelby"/>
            <author fullname="K. Hartke" initials="K." surname="Hartke"/>
            <author fullname="C. Bormann" initials="C." surname="Bormann"/>
            <date month="June" year="2014"/>
            <abstract>
              <t indent="0">The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation.</t>
              <t indent="0">CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7252"/>
          <seriesInfo name="DOI" value="10.17487/RFC7252"/>
        </reference>
      </references>
    </references>
    <section anchor="Acknowledgments" numbered="false" toc="include" removeInRFC="false" pn="section-appendix.a">
      <name slugifiedName="name-acknowledgments">Acknowledgments</name>
      <t indent="0" pn="section-appendix.a-1">This document is a product of the ACE Working Group of the IETF.
      Special thanks to <contact fullname="Brian Campbell"/> for his thorough review of
      this document.</t>
      <t indent="0" pn="section-appendix.a-2"><contact fullname="Ludwig Seitz"/> worked on this document as part of the
      CelticNext projects CyberWI and CRITISEC with funding from Vinnova.</t>
    </section>
    <section anchor="authors-addresses" numbered="false" removeInRFC="false" toc="include" pn="section-appendix.b">
      <name slugifiedName="name-authors-address">Author's Address</name>
      <author fullname="Ludwig Seitz" initials="L." surname="Seitz">
        <organization showOnFrontPage="true">Combitech</organization>
        <address>
          <postal>
            <street>Djäknegatan 31</street>
            <code>211 35</code>
            <city>Malmö</city>
            <country>Sweden</country>
          </postal>
          <email>ludwig.seitz@combitech.com</email>
        </address>
      </author>
    </section>
  </back>
</rfc>
