Network Working Group C. Wendt Internet-Draft D. Hancock Intended status: Standards Track Somos Inc. Expires: 25 September 2026 24 March 2026 JWTClaimConstraints profile of ACME Authority Token draft-ietf-acme-authority-token-jwtclaimcon-01 Abstract This document defines an authority token profile for the validation of JWTClaimConstraints and EnhancedJWTClaimConstraints certificate extensions within the Automated Certificate Management Environment (ACME) protocol. This profile is based on the Authority Token framework and establishes the specific ACME identifier type, challenge mechanism, and token format necessary to authorize a client to request a certificate containing these constraints. 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 25 September 2026. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. Wendt & Hancock Expires 25 September 2026 [Page 1] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 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. ACME Procedures when Challenge requires two Authority Tokens . . . . . . . . . . . . . . . . . . . . . . . 12 6. Validating the JWTClaimConstraints Authority Token . . . . . 13 7. Using ACME-issued Certificates with JSON Web Signature . . . 14 8. Security Considerations . . . . . . . . . . . . . . . . . . . 15 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 11. Normative References . . . . . . . . . . . . . . . . . . . . 16 Appendix A. JWTClaimConstraints Identifier Value Examples . . . 17 A.1. No Extended Claims Authorized . . . . . . . . . . . . . . 18 A.2. Extended Claims Authorized (Uniform Constraints) . . . . 19 A.3. Extended Claims Authorized (Per-TN Subset Constraints) . 20 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 1. Introduction The validation of certificate extensions that constrain the use of a certificate's credentials, such as the JWTClaimConstraints extension defined in [RFC8226] and the EnhancedJWTClaimConstraints extension defined in [RFC9118], is critical for defining the scope of an issued certificate. This document specifies an authority token profile for validating these constraints, modeled after the authority token framework established in [RFC9447] and the TNAuthList validation Wendt & Hancock Expires 25 September 2026 [Page 2] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 defined in [RFC9448]. This profile facilitates proper delegation and authorization for entities requesting certificates under ACME and similar frameworks. It 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 and EnhancedJWTClaimConstraints extensions based on the issuer of the token. This document is intended for use by Secure Telephone Identity (STI) Certification Authorities. In this ecosystem, certificates contain telephone-number-related (TNAuthList) extensions and JWTClaimConstraints extensions defined in [RFC8226] and [RFC9118], and certificate issuance is governed by a set of STI-specific Token Authorities. The TNAuthList Authority Token profile ([RFC9448]) is the parallel specification for telephone number authorization in this ecosystem and is already widely deployed. This document follows the same pattern to address authorization of the JWTClaimConstraints and EnhancedJWTClaimConstraints extensions. ACME implementers unfamiliar with the STIR ecosystem can treat the validation of the JWTClaimConstraints token value as a domain-specific authorization step analogous to TNAuthList validation: the ACME wire protocol mechanics are identical, and the Token Authority is responsible for the domain-specific semantic validation described in [RFC8226] and [RFC9118]. This document also discusses the ability for an 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). 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. Wendt & Hancock Expires 25 September 2026 [Page 3] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 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 or EnhancedJWTClaimConstraints extension requested. 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: "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 Wendt & Hancock Expires 25 September 2026 [Page 4] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 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. 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. 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" } Wendt & Hancock Expires 25 September 2026 [Page 5] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 HTTP/1.1 200 OK Content-Type: application/json Link: ;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", defined 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. If a "token- authority" parameter is present, the ACME client MAY use this 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, 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. Wendt & Hancock Expires 25 September 2026 [Page 6] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 POST /acme/chall/prV_B7yEyA4 HTTP/1.1 Host: example.com Content-Type: application/jose+json { "protected": base64url({ "alg": "ES256", "kid": "https://example.com/acme/acct/evOfKhNU60wg", "nonce": "Q_s3MWoqT05TrdkM2MTDcw", "url": "https://example.com/acme/chall/prV_B7yEyA4" }), "payload": base64url({ "tkauth": "DGyRejmCefe7v4N...vb29HhjjLPSggwiE" }), "signature": "9cbg5JO1Gf5YLjjz...SpkUfcdPai9uVYYQ" } The "tkauth" field in the challenge response object is specific to the tkauth-01 challenge type. When responding to a challenge for a JWTClaimConstraints identifier, this field SHALL 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. 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. Wendt & Hancock Expires 25 September 2026 [Page 7] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 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 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 fingerprint 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: Wendt & Hancock Expires 25 September 2026 [Page 8] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 { "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". Note that this account identifier refers to the ACME client's account with the Token Authority, and is distinct from the ACME account used with the CA. There is assumed to 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: Wendt & Hancock Expires 25 September 2026 [Page 9] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 { "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"} The ACME client then uses the value of the "token" field as the "tkauth" field in the challenge response POST to the ACME challenge URL, as described in Section 4. 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. Wendt & Hancock Expires 25 September 2026 [Page 10] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 The fingerprint in the token request is not meant to be verified by the Token Authority. Rather, it 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 that the token requested and used came from the same party that controls the ACME client. 5.4. Scope of the JWTClaimConstraints Because this specification involves the JWTClaimConstraints and EnhancedJWTClaimConstraints extensions, the client MAY request an Authority Token with some subset of its own authority as the JWTClaimConstraints provided in the "tkvalue" element of the "atc" JSON object. JWTClaimConstraints can be constructed to define a limited scope of claims and claim values the client has authority over. 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], a certificate order may require two Authority Token identifier types: * 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 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. Since these two certificate extensions constrain the resources and claims available to the certificate, there is an inherent interaction between these two types of Authority Tokens. Wendt & Hancock Expires 25 September 2026 [Page 11] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 The "value" field of the JWTClaimConstraints identifier, and the corresponding "tkvalue" in the "atc" claim, is a base64url-encoded DER representation of a JWTClaimConstraints or EnhancedJWTClaimConstraints ASN.1 object as defined in [RFC8226] and [RFC9118]. From the ACME server's perspective this value is opaque: validation step 5 in Section 6 requires only that the value in the token matches the value in the order. The semantic content of the extension — which claims are permitted or excluded, and for which telephone numbers — is a STIR ecosystem concern governed by [RFC8226] and [RFC9118], and is validated by the Token Authority prior to token issuance (see Section 5.3). Informative examples of JWTClaimConstraints ASN.1 structures, their DER encodings, and corresponding base64url values are provided in Appendix A. 5.5.1. ACME Procedures when Challenge requires two Authority Tokens Sections 3 and 4 describe the ACME procedures for issuing a certificate based on 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 includes both identifier types: "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, one for each identifier: "authorizations": [ "https://example.com/acme/authz/1234", "https://example.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. Wendt & Hancock Expires 25 September 2026 [Page 12] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 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. Steps 1 through 3 and steps 6 through 8 are general ACME authority token validation steps applicable to any Authority Token profile. Steps 4 and 5 are specific to the JWTClaimConstraints profile. The semantic validation of whether the JWTClaimConstraints or EnhancedJWTClaimConstraints content accurately reflects the requesting party's authorized resources is the responsibility of the Token Authority prior to issuing the token (see Section 5.3), and is governed by [RFC8226] and [RFC9118]. 1. Verify that the value of the "atc" claim is a well-formed JSON object containing the mandatory key values ("tktype", "tkvalue", "fingerprint"). 2. Verify Token Issuer: If there is an "x5u" parameter, verify the "x5u" parameter is an HTTPS URL with a reference to a certificate representing the trusted issuer of authority tokens. If there is an "x5c" parameter, verify the certificate array contains a certificate representing the trusted issuer of authority tokens. 3. Verify Signature: Verify the JWTClaimConstraints Authority Token signature using the public key of the certificate referenced by the token's "x5u" or "x5c" parameter. 4. Verify Token Type: Verify that the "atc" claim contains a "tktype" identifier with the value "JWTClaimConstraints". 5. Verify Constraints Match: 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. 6. Verify Claims: Verify that the remaining claims are valid (e.g., verify that the token has not expired using the "exp" claim). 7. Verify Account Control: Verify that the "atc" claim "fingerprint" is valid and matches the account key of the client making the request. 8. Verify CA Flag: Verify that the "atc" claim "ca" identifier boolean corresponds to the CA boolean in the Basic Constraints extension in the Certificate Signing Request (CSR) for either a CA certificate or an end-entity certificate. Wendt & Hancock Expires 25 September 2026 [Page 13] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 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) objects can include an "x5u" header parameter to refer to a certificate for signature validation. In order to support this usage, the Certificate Authority (CA) MAY host the newly issued certificate and provide a URL that the ACME client owner can directly reference in the "x5u" header parameter of their signed JWS objects. To facilitate this, the CA MAY add a newly defined field called "x5u" to the 200 (OK) order object response when the certificate is ready for the finalize request: x5u (optional, string): A URL that can be used to reference the certificate in the "x5u" parameter of a JWS object. An example of a 200 (OK) response containing the new "x5u" field: Wendt & Hancock Expires 25 September 2026 [Page 14] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 HTTP/1.1 200 OK Content-Type: application/json Replay-Nonce: CGf81JWBsq8QyIgPCi9Q9X Link: ;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://example.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 JWTClaimConstraints and EnhancedJWTClaimConstraints, which constrain the resources and claims a certificate holder can assert. 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 or misuse the constrained resources. This document inherits the security properties of [RFC9447]. Implementations SHOULD follow the best practices identified in [RFC8725] for cryptographic security. 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. Wendt & Hancock Expires 25 September 2026 [Page 15] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 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. 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, . [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, . [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, . [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May 2015, . [RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token (JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Wendt & Hancock Expires 25 September 2026 [Page 16] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 [RFC8226] Peterson, J. and S. Turner, "Secure Telephone Identity Credentials: Certificates", RFC 8226, DOI 10.17487/RFC8226, February 2018, . [RFC8555] Barnes, R., Hoffman-Andrews, J., McCarney, D., and J. Kasten, "Automatic Certificate Management Environment (ACME)", RFC 8555, DOI 10.17487/RFC8555, March 2019, . [RFC8725] Sheffer, Y., Hardt, D., and M. Jones, "JSON Web Token Best Current Practices", BCP 225, RFC 8725, DOI 10.17487/RFC8725, February 2020, . [RFC9060] Peterson, J., "Secure Telephone Identity Revisited (STIR) Certificate Delegation", RFC 9060, DOI 10.17487/RFC9060, September 2021, . [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, . [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, . [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, . Appendix A. JWTClaimConstraints Identifier Value Examples This appendix provides informative examples of JWTClaimConstraints and EnhancedJWTClaimConstraints ASN.1 structures as defined in [RFC8226] and [RFC9118], along with their DER encodings and base64url values as used in the ACME identifier "value" field and the "tkvalue" of the "atc" claim. These examples are intended for implementers of STI Token Authorities and certificate requestors in the STIR/SHAKEN ecosystem. ACME server implementations treat the identifier value as opaque and are not required to parse or validate its internal structure. Wendt & Hancock Expires 25 September 2026 [Page 17] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 Note: single-quote delimiters in the ASN.1 notation below denote string values; inner double quotes are part of the JSON-formatted claim values as defined in [RFC8226]. A.1. No Extended Claims Authorized In this case, the requestor is authorized to use a set of telephone numbers but no optional claim information. The EnhancedJWTClaimConstraints extension uses a mustExclude constraint to prohibit all optional claims relevant to the application. SEQUENCE { mustExclude [2] { SEQUENCE { IA5String 'attest' IA5String 'origid' IA5String 'div' IA5String 'rph' IA5String 'sph' IA5String 'rcd' IA5String 'rcdi' IA5String 'crn' } } } DER encoding (51 bytes, hex): 30 31 a2 2f 16 06 61 74 74 65 73 74 16 06 6f 72 69 67 69 64 16 03 64 69 76 16 03 72 70 68 16 03 73 70 68 16 03 72 63 64 16 04 72 63 64 69 16 03 63 72 6e base64url value: MDGiLxYGYXR0ZXN0FgZvcmlnaWQWA2RpdhYDcnBoFgNzcGgWA3JjZBYEcmNkaRYDY3Ju A simpler alternative for requestors not authorized to include optional claims is to submit a new-order request containing only a TNAuthList identifier. In this case, the absence of a JWTClaimConstraints identifier MAY trigger local policy in the CA to include a restrictive EnhancedJWTClaimConstraints extension in the issued certificate. Wendt & Hancock Expires 25 September 2026 [Page 18] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 A.2. Extended Claims Authorized (Uniform Constraints) In this case, the requestor is authorized to assert a specific set of claim information that applies uniformly across all authorized telephone numbers. The extension uses a permittedValues constraint for the authorized claims and a mustExclude constraint for the remainder. 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' } } } DER encoding (104 bytes, hex): 30 66 a1 3d 30 3b 30 39 16 03 72 63 64 30 15 0c 13 22 6e 61 6d 22 3a 20 22 4a 61 6d 65 73 20 42 6f 6e 64 22 16 03 63 72 6e 30 16 0c 14 22 46 6f 72 20 79 6f 75 72 20 65 61 72 73 20 6f 6e 6c 79 22 a2 25 16 06 61 74 74 65 73 74 16 06 6f 72 69 67 69 64 16 03 64 69 76 16 03 72 70 68 16 03 73 70 68 16 04 72 63 64 69 base64url value: Wendt & Hancock Expires 25 September 2026 [Page 19] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 MGahPTA7MDkWA3JjZDAVDBMibmFtIjogIkphbWVzIEJvbmQiFgNjcm4wFgwUIkZv ciB5b3VyIGVhcnMgb25seSKiJRYGYXR0ZXN0FgZvcmlnaWQWA2RpdhYDcnBoFgNz cGgWBHJjZGk A.3. Extended Claims Authorized (Per-TN Subset Constraints) In this case, the requestor is authorized to assert different sets of claims for distinct subsets of telephone numbers. This is expressed by including an "orig" claim in the permittedValues entry to associate specific claim values with a particular set of telephone numbers. 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' } } } DER encoding (143 bytes, hex): Wendt & Hancock Expires 25 September 2026 [Page 20] Internet-Draft ACME JWTClaimConstraints Auth Token March 2026 30 81 8c a1 63 30 61 30 5f 16 03 72 63 64 30 15 0c 13 22 6e 61 6d 22 3a 20 22 4a 61 6d 65 73 20 42 6f 6e 64 22 16 03 63 72 6e 30 16 0c 14 22 46 6f 72 20 79 6f 75 72 20 65 61 72 73 20 6f 6e 6c 79 22 16 04 6f 72 69 67 30 1e 0c 0d 22 31 32 30 32 35 35 35 31 30 30 30 22 0c 0d 22 31 32 30 32 35 35 35 31 30 30 31 22 a2 25 16 06 61 74 74 65 73 74 16 06 6f 72 69 67 69 64 16 03 64 69 76 16 03 72 70 68 16 03 73 70 68 16 04 72 63 64 69 base64url value: MIGMoWMwYTBfFgNyY2QwFQwTIm5hbSI6ICJKYW1lcyBCb25kIhYDY3JuMBYMFCJG b3IgeW91ciBlYXJzIG9ubHkiFgRvcmlnMB4MDSIxMjAyNTU1MTAwMCIMDSIxMjAy NTU1MTAwMSKiJRYGYXR0ZXN0FgZvcmlnaWQWA2RpdhYDcnBoFgNzcGgWBHJjZGk 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 Wendt & Hancock Expires 25 September 2026 [Page 21]