



Network Working Group                                           C. Wendt
Internet-Draft                                                D. Hancock
Intended status: Standards Track                              Somos Inc.
Expires: 8 January 2026                                      7 July 2025


          JWTClaimConstraints profile of ACME Authority Token
            draft-wendt-acme-authority-token-jwtclaimcon-03

Abstract

   This document defines an authority token profile for handling the
   validation of JWTClaimConstraints and EnhancedJWTClaimConstraints.
   This profile follows the model established in Authority Token for the
   validation of TNAuthList but is specifically tailored for the
   JWTClaimConstraints certificate extensions.  The profile enables
   validation and challenge processes necessary to support certificates
   containing both TNAuthList and JWTClaimConstraints, particularly in
   the context of Secure Telephone Identity (STI).

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 8 January 2026.

Copyright Notice

   Copyright (c) 2025 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
   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  ACME new-order Identifiers for JWTClaimConstraints  . . . . .   3
   4.  JWTClaimConstraints Authorization . . . . . . . . . . . . . .   5
   5.  JWTClaimConstraints Authority Token . . . . . . . . . . . . .   7
     5.1.  JWTClaimConstraints Authority Token Payload . . . . . . .   7
       5.1.1.  "iss" claim . . . . . . . . . . . . . . . . . . . . .   7
       5.1.2.  "exp" claim . . . . . . . . . . . . . . . . . . . . .   8
       5.1.3.  "jti" claim . . . . . . . . . . . . . . . . . . . . .   8
       5.1.4.  "atc" claim . . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Acquiring the token from the Token Authority  . . . . . .   9
     5.3.  Token Authority Responsibilities  . . . . . . . . . . . .  10
     5.4.  Scope of the JWTClaimConstraints  . . . . . . . . . . . .  11
     5.5.  ACME Challenges requiring multiple Authority Tokens . . .  11
       5.5.1.  Examples of ACME Challenges requiring two Authority
               Tokens  . . . . . . . . . . . . . . . . . . . . . . .  12
       5.5.2.  ACME Procedures when Challenge requires two Authority
               Tokens  . . . . . . . . . . . . . . . . . . . . . . .  15
   6.  Validating the JWTClaimConstraints Authority Token  . . . . .  16
   7.  Using ACME-issued Certificates with JSON Web Signature  . . .  17
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  18
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  19
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     11.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   The validation of JWTClaimConstraints as part of an STI certificate
   defined in [RFC8226] is critical for ensuring the integrity and scope
   of claims used in PASSporTs.  This document specifies an authority
   token profile for validating JWTClaimConstraints, modeled after the
   authority token framework established in [RFC9447] and the TNAuthList
   validation defined in [RFC9448].  This profile facilitates proper
   delegation and authorization for entities requesting certificates



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   under ACME [RFC8555] and similar frameworks.

   This Authority Token profile specifically addresses the inclusions of
   the STI certificate extensions JWTClaimConstraints, as defined in
   [RFC8226], and EnhancedJWTClaimConstraints, as defined in [RFC9118].
   The STI certificate credentials are used to sign PASSporTs [RFC8225],
   which can be carried in using protocols such as SIP [RFC8224].  This
   document defines the use of the JWTClaimConstraints Authority Token
   in the ACME challenge to prove an authoritative or trusted use of the
   contents of the JWTClaimConstraints based on the issuer of the token.
   The Certification Authority (CA) issuing the STI Certificate can be
   informed of the proper use and contents of the JWTClaimConstraints
   extension based on the STI eco-system policies, best practices, or
   authoritative information which is out of scope of this document and
   will be defined by the STI eco-system.

   This document also discusses the ability for a telephone authority to
   authorize the creation of CA types of certificates for delegation as
   defined in [RFC9060].

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.

3.  ACME new-order Identifiers for JWTClaimConstraints

   In [RFC8555], Section 7 defines the procedure that an ACME client
   uses to order a new certificate from a Certification Authority (CA).
   The new-order request contains an "identifiers" field that specifies
   the identifier objects the order corresponds to.  This draft defines
   a new type of identifier object called JWTClaimConstraints.  A
   JWTClaimConstraints identifier contains the Token Claim Constraints
   information to be populated in the JWTClaimConstraints or
   EnhancedJWTClaimConstraints of the new certificate.  For the
   JWTClaimConstraints identifier, the new-order request includes a type
   set to the string "JWTClaimConstraints".  The value of the
   JWTClaimConstraints identifier MUST be set to the details of the
   JWTClaimConstraints requested.









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   The format of the string that represents the JWTClaimConstraints MUST
   be constructed using base64url encoding, as per [RFC8555] base64url
   encoding described in Section 5 of [RFC4648] according to the profile
   specified in JSON Web Signature in Section 2 of [RFC7515].  The
   base64url encoding MUST NOT include any padding characters and the
   JWTClaimConstraints ASN.1 object MUST be encoded using DER encoding
   rules.

   An example of an ACME order object "identifiers" field containing a
   JWTClaimConstraints certificate would look as follows,

    "identifiers": [{"type":"JWTClaimConstraints",
      "value":"F83n2a...avn27DN3"}]

   where the "value" object string represents the arbitrary length
   base64url encoded string.

   A full new-order request would look as follows,

   POST /acme/new-order HTTP/1.1
   Host: example.com
   Content-Type: application/jose+json

   {
     "protected": base64url({
       "alg": "ES256",
       "kid": "https://example.com/acme/acct/evOfKhNU60wg",
       "nonce": "5XJ1L3lEkMG7tR6pA00clA",
       "url": "https://example.com/acme/new-order"
     }),
     "payload": base64url({
       "identifiers": [{"type":"JWTClaimConstraints",
         "value":"F83n...n27DN3"}],
       "notBefore": "2025-01-01T00:00:00Z",
       "notAfter": "2025-01-08T00:00:00Z"
     }),
     "signature": "H6ZXtGjTZyUnPeKn...wEA4TklBdh3e454g"
   }

   On receiving a valid new-order request, the ACME server creates an
   authorization object, [RFC8555] Section 7.1.4, containing the
   challenge that the ACME client must satisfy to demonstrate authority
   for the identifiers specified by the new order (in this case, the
   JWTClaimConstraints identifier).  The CA adds the authorization
   object URL to the "authorizations" field of the order object, and
   returns the order object to the ACME client in the body of a 201
   (Created) response.




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   HTTP/1.1 201 Created
   Content-Type: application/json
   Replay-Nonce: MYAuvOpaoIiywTezizk5vw
   Location: https://example.com/acme/order/1234

   {
     "status": "pending",
     "expires": "2025-01-08T00:00:00Z",

     "notBefore": "2025-01-01T00:00:00Z",
     "notAfter": "2025-01-08T00:00:00Z",
     "identifiers":[{"type":"JWTClaimConstraints",
                    "value":"F83n2a...avn27DN3"}],

     "authorizations": [
      "https://example.com/acme/authz/1234"
     ],
     "finalize": "https://example.com/acme/order/1234/finalize"
   }

4.  JWTClaimConstraints Authorization

   On receiving the new-order response, the ACME client queries the
   referenced authorization object to obtain the challenges for the
   identifier contained in the new-order request as shown in the
   following example request and response.

   POST /acme/authz/1234 HTTP/1.1
       Host: example.com
       Content-Type: application/jose+json

       {
         "protected": base64url({
           "alg": "ES256",
           "kid": " https://example.com/acme/acct/evOfKhNU60wg",
           "nonce": "uQpSjlRb4vQVCjVYAyyUWg",
           "url": "https://example.com/acme/authz/1234"
         }),
         "payload": "",
         "signature": "nuSDISbWG8mMgE7H...QyVUL68yzf3Zawps"
       }










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   HTTP/1.1 200 OK
   Content-Type: application/json
   Link: <https://example.com/acme/some-directory>;rel="index"

   {
     "status": "pending",
     "expires": "2025-01-08T00:00:00Z",

     "identifier": {
       "type:"JWTClaimConstraints",
       "value":"F83n2a...avn27DN3"
     },

     "challenges": [
       {
         "type": "tkauth-01",
         "tkauth-type": "atc",
         "token-authority": "https://authority.example.org",
         "url": "https://boulder.example.com/acme/chall/prV_B7yEyA4",
         "token": "IlirfxKKXAsHtmzK29Pj8A"
       }
     ]
   }

   When processing a certificate order containing an identifier of type
   "JWTClaimConstraints", a CA uses the Authority Token challenge type
   of "tkauth-01" with a "tkauth-type" of "atc" in [RFC9447] to verify
   that the requesting ACME client has authenticated and authorized
   control over the requested resources represented by the
   "JWTClaimConstraints" value.

   The challenge "token-authority" parameter is optional and is only
   used in cases where the VoIP telephone network requires the CA to
   identify the Token Authority.  If a "token-authority" parameter is
   present, then the ACME client MAY use the "token-authority" value to
   identify the URL representing the Token Authority that will provide
   the JWTClaimConstraints Authority Token response to the challenge.
   If the "token-authority" parameter is not present, then the ACME
   client MUST identify the Token Authority based on locally configured
   information or local policies.

   The ACME client responds to the challenge by posting the
   JWTClaimConstraints Authority Token to the challenge URL identified
   in the returned ACME authorization object, an example of which
   follows.






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   POST /acme/chall/prV_B7yEyA4 HTTP/1.1
   Host: boulder.example.com
   Content-Type: application/jose+json

   {
     "protected": base64url({
     "alg": "ES256",
     "kid": "https://example.com/acme/acct/evOfKhNU60wg",
     "nonce": "Q_s3MWoqT05TrdkM2MTDcw",
     "url": "https://boulder.example.com/acme/authz/asdf/0"
     }),
     "payload": base64url({
     "tkauth": "DGyRejmCefe7v4N...vb29HhjjLPSggwiE"
     }),
     "signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ"
   }

   The "tkauth" field in the challenge object is defined in [RFC9448].
   It is specific to the tkauth-01 challenge type, and when responding
   to a challenge for a JWTClaimConstraints identifier, that should
   contain the JWTClaimConstraints Authority Token defined in the next
   section.

5.  JWTClaimConstraints Authority Token

   The JWTClaimConstraints Authority Token is a profile instance of the
   ACME Authority Token defined in [RFC9447].

   The JWTClaimConstraints Authority Token Protected header MUST comply
   with the Authority Token Protected header as defined in [RFC9447].

5.1.  JWTClaimConstraints Authority Token Payload

   The JWTClaimConstraints Authority Token Payload MUST include the
   mandatory claims "exp", "jti", and "atc", and MAY include the
   optional claims defined for the Authority Token detailed in the next
   subsections.

5.1.1.  "iss" claim

   The "iss" claim is an optional claim defined in [RFC7519]
   Section 4.1.1.  It can be used as a URL identifying the Token
   Authority that issued the JWTClaimConstraints Authority Token beyond
   the "x5u" or other Header claims that identify the location of the
   certificate or certificate chain of the Token Authority used to
   validate the JWTClaimConstraints Authority Token.





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5.1.2.  "exp" claim

   The "exp" claim, defined in [RFC7519] Section 4.1.4, MUST be included
   and contains the DateTime value of the ending date and time that the
   JWTClaimConstraints Authority Token expires.

5.1.3.  "jti" claim

   The "jti" claim, defined in [RFC7519] Section 4.1.7, MUST be included
   and contains a unique identifier for this JWTClaimConstraints
   Authority Token transaction.

5.1.4.  "atc" claim

   The "atc" claim MUST be included and is defined in [RFC9447].  It
   contains a JSON object with the following elements:

   *  a "tktype" key with a string value equal to "JWTClaimConstraints"
      to represent a JWTClaimConstraints profile of the authority token
      [RFC9447] defined by this document. "tktype" is a required key and
      MUST be included.

   *  a "tkvalue" key with a string value equal to the base64url
      encoding of the JWTClaimConstraints or EnhancedJWTClaimConstraints
      certificate extension ASN.1 object using DER encoding rules.
      "tkvalue" is a required key and MUST be included.

   *  a "ca" key with a boolean value set to false (since per [RFC8226]
      the JWTClaimConstraints extension is applicable only to end-entity
      certificates). "ca" is an optional key, if not included the "ca"
      value is considered false by default.

   *  a "fingerprint" key is constructed as defined in [RFC8555]
      Section 8.1 corresponding to the computation of the "Thumbprint"
      step using the ACME account key credentials. "fingerprint" is a
      required key and MUST be included.

   An example of the JWTClaimConstraints Authority Token is as follows:













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   {
     "protected": base64url({
       "typ":"JWT",
       "alg":"ES256",
       "x5u":"https://authority.example.org/cert"
     }),
     "payload": base64url({
       "iss":"https://authority.example.org",
       "exp":1640995200,
       "jti":"id6098364921",
       "atc":{"tktype":"JWTClaimConstraints",
         "tkvalue":"F83n2a...avn27DN3",
         "ca":false,
         "fingerprint":"SHA256 56:3E:CF:AE:83:CA:4D:15:B0:29:FF:1B:71:
          D3:BA:B9:19:81:F8:50:9B:DF:4A:D4:39:72:E2:B1:F0:B9:38:E3"}
     }),
     "signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ"
   }

5.2.  Acquiring the token from the Token Authority

   Following [RFC9447] Section 5, the authority token should be acquired
   using a RESTful HTTP POST transaction as follows:

     POST /at/account/:id/token HTTP/1.1
     Host: authority.example.org
     Content-Type: application/json

   The request will pass the account id as a string in the request
   parameter "id".  This string will be managed as an identifier
   specific to the Token Authority's relationship with the entity that
   is creating and signing a PASSporT [RFC8225] and making the
   Certificate Signing Request via ACME.  There is assumed to also be a
   corresponding authentication procedure that can be verified for the
   success of this transaction.  For example, an HTTP Authorization
   header field containing valid authorization credentials as defined in
   [RFC7231] Section 14.8.

   The body of the POST request MUST contain a JSON object with key
   value pairs corresponding to values that are requested as the content
   of the claims in the issued token.  As an example, the body SHOULD
   contain a JSON object as follows:









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    {
      "atc": {
        "tktype":"JWTClaimConstraints",
        "tkvalue":"F83n2a...avn27DN3",
        "ca":false,
        "fingerprint":"SHA256 56:3E:CF:AE:83:CA:4D:15:B0:29:FF:1B:71:D3
          :BA:B9:19:81:F8:50:9B:DF:4A:D4:39:72:E2:B1:F0:B9:38:E3"
      }
    }

   The response to the POST request if successful returns a 200 OK with
   a JSON body that contains, at a minimum, the JWTClaimConstraints
   Authority Token as a JSON object with a key of "token" and the
   base64url encoded string representing the atc token.  JSON is easily
   extensible, so users of this specification may want to pass other
   pieces of information relevant to a specific application.

   An example successful response would be as follows:

   HTTP/1.1 200 OK
   Content-Type: application/json

   {"token": "DGyRejmCefe7v4N...vb29HhjjLPSggwiE"}

   If the request is not successful, the response should indicate the
   error condition.  Specifically, for the case that the authorization
   credentials are invalid or if the Account ID provided does not exist,
   the response code MUST be 403 - Forbidden.  Other 4xx and 5xx
   responses MUST follow standard [RFC7231] HTTP error condition
   conventions.

5.3.  Token Authority Responsibilities

   When creating the JWTClaimConstraints Authority Token, the Token
   Authority MUST validate that the information contained in the ASN.1
   JWTClaimConstraints accurately represents the corresponding
   JWTClaimConstraint resources the requesting party is authorized to
   represent based on their pre-established and verified secure
   relationship between the Token Authority and the requesting party.
   Note that the fingerprint in the token request is not meant to be
   verified by the Token Authority, but rather is meant to be signed as
   part of the token so that the party that requests the token can, as
   part of the challenge response, allow the ACME server to validate the
   token requested and used came from the same party that controls the
   ACME client.






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5.4.  Scope of the JWTClaimConstraints

   Because this specification specifically involves the
   JWTClaimConstraints and EnhancedJWTClaimConstraints defined in
   [RFC8226] and [RFC9118] which involves the required or disallowed
   different claim types or claim values, the client may also request an
   Authority Token with some subset of its own authority as the
   JWTClaimConstraints provided in the "tkvalue" element in the "atc"
   JSON object.  JWTClaimConstraints can be constructed to define a
   limited scope of claims and claim values the client has authority
   over.

   As recommended in [RFC9447] security considerations, an Authority
   Token can either have a scope that attests all of the resources which
   a client is eligible to receive certificates for, or potentially a
   more limited scope that is intended to capture only those resources
   for which a client will receive a certificate from a particular
   certification authority.  Any certification authority that sees an
   Authority Token can learn information about the resources a client
   can claim.  In cases where this incurs a privacy risk, Authority
   Token scopes should be limited to only the resources that will be
   attested by the requested ACME certificate.

5.5.  ACME Challenges requiring multiple Authority Tokens

   The ACME new-order request may include multiple identifiers, each of
   which is authorized separately.  With the introduction of this
   specification, for STIR certificates [RFC8226] two identifier types
   are authorized using Authority Tokens:

   *  The JWTClaimConstraints identifier defined in this document, and

   *  The TNAuthList identifier defined in [RFC9448].

   Other Authority Token types may be introduced in future Authority
   Token profile specifications with similar requirements.

   This section describes scenarios where a new-order request contains
   both of these identifier types.  In such cases, the CA requires the
   ACME client to provide both a JWTClaimConstraints Authority Token and
   a TNAuthList Authority Token as part of the challenge response.

   The TNAuthList Authority Token authorizes the token holder to obtain
   certificates containing a TNAuthList extension whose scope is less
   than or equal to the scope of the TNAuthList identifier in the token.
   The issued certificate then bestows on the holder the authority to
   sign PASSporTs containing an "orig" claim that is within the scope of
   the certificate's TNAuthList extension.



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   As described in section 5, the JWTClaimConstraints Authority Token
   authorizes the token holder to obtain a certificate containing a
   JWTClaimConstraints or EnhancedJWTClaimConstraints extension,
   provided that the extension is within the scope of the
   JWTClaimConstraints identifier in the token.  These two certificate
   extensions constrain the claims and claim values that may appear in
   PASSporTs signed using the certificate's credentials.  In particular,
   claim-constraints extensions can restrict the values of the PASSporT
   "orig" claim, which is also governed by the TNAuthList Authority
   Token.  Accordingly, there is an inherent interaction between these
   two types of Authority Tokens.

5.5.1.  Examples of ACME Challenges requiring two Authority Tokens

   In the examples that follow, the requesting user is authorized to use
   a set of telephone numbers (TNs) and may, depending on the specific
   case, be authorized to assert additional claims and claim values such
   as Rich Call Data (RCD) items within signed PASSporTs.  To support
   these capabilities, the user obtains both a TNAuthList Authority
   Token and a JWTClaimConstraints Authority Token from the appropriate
   Token Authority.  These two tokens may be issued by the same Token
   Authority or by distinct entities.

   The following sub-sections describe three use-cases that illustrate
   how the two types of Authority Tokens can be used to form the ACME
   challenge response to the issuing CA.  In all three cases, the
   TNAuthList Authority Token specifies the TNs, or a subset thereof,
   for which the user is authorized.  The content of the
   JWTClaimConstraints Authority Token varies per use case based on the
   user's authority to assert extended PASSporT claims in addition to
   the authorization provided by the TNAuthList Authority Token.

5.5.1.1.  No Extended Claims Authorized

   In the first case, the requesting user is authorized to use a set of
   TN(s), but no other information conveyed in extended PASSporT claims.
   Accordingly, the JWTClaimConstraints Authority Token contains an
   EnhancedJWTClaimConstraints extension that prohibits all claims
   defined by PASSporT extensions, as shown in the following example:












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   SEQUENCE {
     mustExclude [2] {
       SEQUENCE {
         IA5String 'attest'
         IA5String 'origid'
         IA5String 'div'
         IA5String 'rph'
         IA5String 'sph'
         IA5String 'rcd'
         IA5String 'rcdi'
         IA5String 'crn'
         }
       }
     }

   As described in Section 5.5.2, the CA requires two Authority Tokens
   in the ACME challenge response because the ACME client included both
   a TNAuthList identifier and a JWTClaimConstraints identifier in the
   new-order request.

   A simpler alternative for users not authorized to include extended
   claims in PASSporTs is to submit a new-order request containing only
   a TNAuthList identifier.  In this case, the absence of a
   JWTClaimConstraints identifier could trigger local policy in the CA
   to include the above EnhancedJWTClaimConstraints extension in the
   issued certificate.

5.5.1.2.  Extended Claims Authorized (same claims for all TNs)

   In the second case, the user is authorized to assert extended
   PASSporT claim information, and the additional claim information
   applies to all TN(s) the user is authorized to use.  For example, the
   user could be authorized to use a single set of rich call data
   elements such as a company name and call reason for all authorized
   TNs.  In this case, the corresponding JWTClaimConstraints Authority
   Token contains an EnhancedJWTClaimConstraints extension that permits
   RCD claim values associated with the authorized name and call reason,
   and applies these constraints uniformly across the user's authorized
   TNs, as shown in the following example:












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   SEQUENCE {
     permittedValues [1] {
       SEQUENCE {
         SEQUENCE {
           IA5String 'rcd'
           SEQUENCE {
             UTF8String '"nam": "James Bond"'
             }
           IA5String 'crn'
           SEQUENCE {
             UTF8String '"For your ears only"'
             }
           }
         }
       }
     mustExclude [2] {
       SEQUENCE {
         IA5String 'attest'
         IA5String 'origid'
         IA5String 'div'
         IA5String 'rph'
         IA5String 'sph'
         IA5String 'rcdi'
         }
       }
     }

5.5.1.3.  Extended Claims Authorized (different claims per subset of
          TNs)

   In the third case, the user is permitted to assert different sets of
   extended PASSporT claims for distinct subsets of the user's
   authorized TNs.  For example, the user may be authorized to use a
   calling name and call reason for one subset of authorized TN(s), and
   a different calling name and call reason for a different subset of
   authorized TN(s).  In this example, the JWTClaimConstraints Authority
   Token includes permitted values for the RCD claims that are
   associated with a specific set of TN(s).  Additionally, to ensure
   that the correct set of RCD claims is used with the correct set of
   TNs, the token includes an EnhancedJWTClaimConstraints permitted
   value(s) entry for the "orig" claim which identifies the relevant
   TN(s) to which the RCD claim values apply, as shown in the following
   example:








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   SEQUENCE {
     permittedValues [1] {
       SEQUENCE {
         SEQUENCE {
           IA5String 'rcd'
           SEQUENCE {
             UTF8String '"nam": "James Bond"'
             }
           IA5String 'crn'
           SEQUENCE {
             UTF8String '"For your ears only"'
             }
           IA5String 'orig'
           SEQUENCE {
             UTF8String '"12025551000"'
             UTF8String '"12025551001"'
             }
           }
         }
       }
     mustExclude [2] {
       SEQUENCE {
         IA5String 'attest'
         IA5String 'origid'
         IA5String 'div'
         IA5String 'rph'
         IA5String 'sph'
         IA5String 'rcdi'
         }
       }
     }

   In this case, the CA will verify that the TNAuthList extension of the
   requested certificate is within the scope of both tokens provided in
   the ACME challenge response.

5.5.2.  ACME Procedures when Challenge requires two Authority Tokens

   Sections 3 and 4 describe the ACME procedures for issuing a
   certificate based on receiving a new-order request with an
   "identifier" field containing a single JWTClaimConstraints
   identifier.  This section describes how these procedures are modified
   to support the case where the new-order request contains both a
   TNAuthList and JWTClaimConstraints identifier.

   First, the "identifiers" field in the new-order request is as shown
   in section 3 with the exception that a TNAuthList identifier is added
   to the new-order "identifiers" field, as follows:



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        "identifiers": [
          {"type":"TNAuthList",
           "value":"KHn6xf...jw4A1vgh"}
          {"type":"JWTClaimConstraints",
           "value":"F83n2a...avn27DN3"}]

   The CA includes two "authorizations" URLs in the 201 (Created)
   response to the new-order request, as follows:

        "authorizations": [
           "https://sti-ca.com/acme/authz/1234",
           "https://sti-ca.com/acme/authz/5678"]

   The ACME client then queries each "authorizations" URL as shown in
   section 4.  The CA returns the Authority Token challenge for each
   identifier.  The ACME client responds to each challenge by providing
   an Authority Token of the appropriate type.

6.  Validating the JWTClaimConstraints Authority Token

   Upon receiving a response to the challenge, the ACME server MUST
   perform the following steps to determine the validity of the
   response.

   *  Verify that the value of the "atc" claim is a well-formed JSON
      object containing the mandatory key values.

   *  If there is an "x5u" parameter verify the "x5u" parameter is a
      HTTPS URL with a reference to a certificate representing the
      trusted issuer of authority tokens for the eco-system.

   *  If there is an "x5c" parameter verify the certificate array
      contains a certificate representing the trusted issuer of
      authority tokens for the eco-system.

   *  Verify the JWTClaimConstraints Authority Token signature using the
      public key of the certificate referenced by the token's "x5u" or
      "x5c" parameter.

   *  Verify that "atc" claim contains a "tktype" identifier with the
      value "JWTClaimConstraints".

   *  Verify that the "atc" claim "tkvalue" identifier contains the
      equivalent base64url encoded JWTClaimConstraints or
      EnhancedJWTClaimConstraints certificate extension string value as
      the Identifier specified in the original challenge.





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   *  Verify that the remaining claims are valid (e.g., verify that
      token has not expired)

   *  Verify that the "atc" claim "fingerprint" is valid and matches the
      account key of the client making the request

   *  Verify that the "atc" claim "ca" identifier boolean corresponds to
      the CA boolean in the Basic Constraints extension in the CSR for
      either CA certificate or end-entity certificate

   If all steps in the token validation process pass, then the ACME
   server MUST set the challenge object "status" to "valid".  If any
   step of the validation process fails, the "status" in the challenge
   object MUST be set to "invalid".

7.  Using ACME-issued Certificates with JSON Web Signature

   JSON Web Signature (JWS, [RFC7515]) objects can include an "x5u"
   header parameter to refer to a certificate that is used to validate
   the JWS signature.  For example, the STIR PASSporT framework
   [RFC8225] uses "x5u" to indicate the STIR certificate used to
   validate the PASSporT JWS object.  The URLs used in "x5u" are
   expected to provide the required certificate in response to a GET
   request, not a POST-as-GET as required for the "certificate" URL in
   the ACME order object.  Thus the current mechanism generally requires
   the ACME client to download the certificate and host it on a public
   URL to make it accessible to relying parties.  This section defines
   an optional mechanism for the Certificate Authority (CA) to host the
   certificate directly and provide a URL that the ACME client owner can
   directly reference in the "x5u" of their signed PASSporTs.

   As described in Section 7.4 of [RFC8555] when the certificate is
   ready for making a finalize request, the server will return a 200
   (OK) with the updated order object.  In this response, an ACME Server
   can add a newly defined field called "x5u" that can pass this URL to
   the ACME client for usage in generated PASSporTs as a publicly
   available URL for PASSporT validation.

   x5u (optional, string):  A URL that can be used to reference the
      certificate in the "x5u" parameter of a JWS object [RFC7515]

   The publishing of the certificates at the new "x5u" URL should follow
   the GET request requirement as mentioned above and should be
   consistent with the timely publication according to the durations of
   the certificate lifecycle.

   The following is an example of the use of "x5u" in the response when
   the certificate status is "valid".



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   HTTP/1.1 200 OK
   Content-Type: application/json
   Replay-Nonce: CGf81JWBsq8QyIgPCi9Q9X
   Link: <https://example.com/acme/directory>;rel="index"
   Location: https://example.com/acme/order/TOlocE8rfgo

   {
     "status": "valid",
     "expires": "2016-01-20T14:09:07.99Z",

     "notBefore": "2016-01-01T00:00:00Z",
     "notAfter": "2016-01-08T00:00:00Z",

     "identifiers": [
       "type":"JWTClaimConstraints",
       "value":"F83n2a...avn27DN3"
     ],

     "authorizations": ["https://sti-ca.com/acme/authz/1234"],

     "finalize": "https://example.com/acme/order/TOlocE8rfgo/finalize",

     "certificate": "https://example.com/acme/cert/mAt3xBGaobw",

     "x5u": "https://example.com/cert-repo/giJI53km23.pem"
   }

8.  Security Considerations

   The token represented by this document has the credentials to
   represent PASSporT claims and claim values.  The creation, transport,
   and any storage of this token MUST follow the strictest of security
   best practices beyond the recommendations of the use of encrypted
   transport protocols in this document to protect it from getting in
   the hands of bad actors with illegitimate intent to impersonate
   telephone numbers.

   This document inherits the security properties of [RFC9447].
   Implementations should follow the best practices identified in
   [RFC8725].

   This document only specifies SHA256 for the fingerprint hash.
   However, the syntax of the fingerprint object would permit other
   algorithms if, due to concerns about algorithmic agility, a more
   robust algorithm were required at a future time.  Future
   specifications can define new algorithms for the fingerprint object
   as needed.




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9.  IANA Considerations

   This document requests the addition of a new identifier object type
   to the "ACME Identifier Types" registry defined in Section 9.7.7 of
   [RFC8555].

   +---------------------+-----------+
   |        Label        | Reference |
   +---------------------+-----------+
   | JWTClaimConstraints |  RFCThis  |
   +---------------------+-----------+

10.  Acknowledgements

   We would like to thank ACME and STIR working groups for valuable
   contributions to the authority token framework used in this document.

11.  References

11.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/rfc/rfc2119>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/rfc/rfc4648>.

   [RFC7231]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
              DOI 10.17487/RFC7231, June 2014,
              <https://www.rfc-editor.org/rfc/rfc7231>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <https://www.rfc-editor.org/rfc/rfc7515>.

   [RFC7519]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
              (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
              <https://www.rfc-editor.org/rfc/rfc7519>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.





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   [RFC8226]  Peterson, J. and S. Turner, "Secure Telephone Identity
              Credentials: Certificates", RFC 8226,
              DOI 10.17487/RFC8226, February 2018,
              <https://www.rfc-editor.org/rfc/rfc8226>.

   [RFC8555]  Barnes, R., Hoffman-Andrews, J., McCarney, D., and J.
              Kasten, "Automatic Certificate Management Environment
              (ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019,
              <https://www.rfc-editor.org/rfc/rfc8555>.

   [RFC8725]  Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best
              Current Practices", BCP 225, RFC 8725,
              DOI 10.17487/RFC8725, February 2020,
              <https://www.rfc-editor.org/rfc/rfc8725>.

   [RFC9060]  Peterson, J., "Secure Telephone Identity Revisited (STIR)
              Certificate Delegation", RFC 9060, DOI 10.17487/RFC9060,
              September 2021, <https://www.rfc-editor.org/rfc/rfc9060>.

   [RFC9118]  Housley, R., "Enhanced JSON Web Token (JWT) Claim
              Constraints for Secure Telephone Identity Revisited (STIR)
              Certificates", RFC 9118, DOI 10.17487/RFC9118, August
              2021, <https://www.rfc-editor.org/rfc/rfc9118>.

   [RFC9447]  Peterson, J., Barnes, M., Hancock, D., and C. Wendt,
              "Automated Certificate Management Environment (ACME)
              Challenges Using an Authority Token", RFC 9447,
              DOI 10.17487/RFC9447, September 2023,
              <https://www.rfc-editor.org/rfc/rfc9447>.

   [RFC9448]  Wendt, C., Hancock, D., Barnes, M., and J. Peterson,
              "TNAuthList Profile of Automated Certificate Management
              Environment (ACME) Authority Token", RFC 9448,
              DOI 10.17487/RFC9448, September 2023,
              <https://www.rfc-editor.org/rfc/rfc9448>.

11.2.  Informative References

   [RFC8224]  Peterson, J., Jennings, C., Rescorla, E., and C. Wendt,
              "Authenticated Identity Management in the Session
              Initiation Protocol (SIP)", RFC 8224,
              DOI 10.17487/RFC8224, February 2018,
              <https://www.rfc-editor.org/rfc/rfc8224>.

   [RFC8225]  Wendt, C. and J. Peterson, "PASSporT: Personal Assertion
              Token", RFC 8225, DOI 10.17487/RFC8225, February 2018,
              <https://www.rfc-editor.org/rfc/rfc8225>.




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Authors' Addresses

   Chris Wendt
   Somos Inc.
   United States of America
   Email: chris@appliedbits.com


   David Hancock
   Somos Inc.
   United States of America
   Email: davidhancock.ietf@gmail.com







































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