



Workload Identity in Multi System Environments               B. Campbell
Internet-Draft                                             Ping Identity
Intended status: Standards Track                              J. Salowey
Expires: 5 January 2026                                         CyberArk
                                                      A. Schwenkschuster
                                                                   SPIRL
                                                              Y. Sheffer
                                                                  Intuit
                                                             4 July 2025


               WIMSE Workload to Workload Authentication
                    draft-ietf-wimse-s2s-protocol-06

Abstract

   The WIMSE architecture defines authentication and authorization for
   software workloads in a variety of runtime environments, from the
   most basic ones up to complex multi-service, multi-cloud, multi-
   tenant deployments.  This document defines the simplest, atomic unit
   of this architecture: the protocol between two workloads that need to
   verify each other's identity in order to communicate securely.  The
   scope of this protocol is a single HTTP request-and-response pair.
   To address the needs of different setups, we propose two protocols,
   one at the application level and one that makes use of trusted TLS
   transport.  These two protocols are compatible, in the sense that a
   single call chain can have some calls use one protocol and some use
   the other.  Workload A can call Workload B with mutual TLS
   authentication, while the next call from Workload B to Workload C
   would be authenticated at the application level.

About This Document

   This note is to be removed before publishing as an RFC.

   The latest revision of this draft can be found at https://ietf-wg-
   wimse.github.io/draft-ietf-wimse-s2s-protocol/draft-ietf-wimse-s2s-
   protocol.html.  Status information for this document may be found at
   https://datatracker.ietf.org/doc/draft-ietf-wimse-s2s-protocol/.

   Discussion of this document takes place on the Workload Identity in
   Multi System Environments Working Group mailing list
   (mailto:wimse@ietf.org), which is archived at
   https://mailarchive.ietf.org/arch/browse/wimse/.  Subscribe at
   https://www.ietf.org/mailman/listinfo/wimse/.

   Source for this draft and an issue tracker can be found at
   https://github.com/ietf-wg-wimse/draft-ietf-wimse-s2s-protocol.



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Status of This Memo

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

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

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 5 January 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Extending This Protocol to Other Use Cases  . . . . . . .   4
     1.2.  Deployment Architecture and Message Flow  . . . . . . . .   4
     1.3.  Workload Identifiers and Authentication Granularity . . .   6
   2.  Conventions and Definitions . . . . . . . . . . . . . . . . .   7
   3.  Application Level Workload To Workload Authentication . . . .   7
     3.1.  The Workload Identity Token . . . . . . . . . . . . . . .   7
       3.1.1.  The WIT HTTP Header . . . . . . . . . . . . . . . . .  10
       3.1.2.  A note on iss claim and key distribution  . . . . . .  11
     3.2.  Option 1: DPoP-Inspired Authentication  . . . . . . . . .  12
     3.3.  Option 2: Authentication Based on HTTP Message
           Signatures  . . . . . . . . . . . . . . . . . . . . . . .  16
     3.4.  Comparing the DPoP Inspired Option with Message
           Signatures  . . . . . . . . . . . . . . . . . . . . . . .  18
     3.5.  Error Conditions  . . . . . . . . . . . . . . . . . . . .  19



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     3.6.  Coexistence with JWT Bearer Tokens  . . . . . . . . . . .  19
   4.  Using Mutual TLS for Workload To Workload Authentication  . .  20
     4.1.  The Workload Identity Certificate . . . . . . . . . . . .  20
     4.2.  Workload Identity Certificate Validation  . . . . . . . .  20
       4.2.1.  Server Name Validation  . . . . . . . . . . . . . . .  21
     4.3.  Client Authorization Using the Workload Identity  . . . .  21
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  21
     5.1.  Workload Identity . . . . . . . . . . . . . . . . . . . .  22
     5.2.  Workload Identity Token and Proof of Possession . . . . .  22
     5.3.  Middle Boxes  . . . . . . . . . . . . . . . . . . . . . .  23
     5.4.  Privacy Considerations  . . . . . . . . . . . . . . . . .  23
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
     6.1.  JSON Web Token Claims . . . . . . . . . . . . . . . . . .  24
     6.2.  Media Type Registration . . . . . . . . . . . . . . . . .  24
       6.2.1.  application/wimse-id+jwt  . . . . . . . . . . . . . .  24
       6.2.2.  application/wimse-proof+jwt . . . . . . . . . . . . .  25
     6.3.  Hypertext Transfer Protocol (HTTP) Field Name
           Registration  . . . . . . . . . . . . . . . . . . . . . .  26
       6.3.1.  Workload-Identity-Token . . . . . . . . . . . . . . .  26
       6.3.2.  Workload-Proof-Token  . . . . . . . . . . . . . . . .  27
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  27
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  28
   Appendix A.  Document History . . . . . . . . . . . . . . . . . .  29
     A.1.  draft-ietf-wimse-s2s-protocol-06  . . . . . . . . . . . .  29
     A.2.  draft-ietf-wimse-s2s-protocol-05  . . . . . . . . . . . .  29
     A.3.  draft-ietf-wimse-s2s-protocol-04  . . . . . . . . . . . .  30
     A.4.  draft-ietf-wimse-s2s-protocol-03  . . . . . . . . . . . .  30
     A.5.  draft-ietf-wimse-s2s-protocol-02  . . . . . . . . . . . .  30
     A.6.  draft-ietf-wimse-s2s-protocol-01  . . . . . . . . . . . .  30
     A.7.  draft-ietf-wimse-s2s-protocol-00  . . . . . . . . . . . .  31
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  31
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31

1.  Introduction

   This document defines authentication and authorization in the context
   of interaction between two workloads.  This is the core component of
   the WIMSE architecture [I-D.ietf-wimse-arch].  For simplicity, this
   document focuses on HTTP-based services, and the workload-to-workload
   call consists of a single HTTP request and its response.  We define
   the credentials that both workloads should possess and how they are
   used to protect the HTTP exchange.

   There are multiple deployment styles in use today, and they result in
   different security properties.  We propose to address them
   differently.




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   *  Many use cases have various middleboxes inserted between pairs of
      workloads, resulting in a transport layer that is not end-to-end
      encrypted.  We propose to address these use cases by protecting
      the HTTP messages at the application level (Section 3).

   *  The other commonly deployed architecture has a mutual-TLS
      connection between each pair of workloads.  This setup can be
      addressed by a simpler solution (Section 4).

   It is an explicit goal of this protocol that a workload deployment
   can include both architectures across a multi-chain call.  In other
   words, Workload A can call Workload B with mutual TLS protection,
   while the next call to Workload C is protected at the application
   level.

   For application-level protection we currently propose two alternative
   solutions, one inspired by DPoP [RFC9449] in Section 3.2 and one
   which is a profile of HTTP Message Signatures [RFC9421] in
   Section 3.3.  The design team believes that we need to pick one of
   these two alternatives for standardization, once we have understood
   their pros and cons.

1.1.  Extending This Protocol to Other Use Cases

   The protocol defined here is narrowly scoped, targeting only HTTP-
   based request/response services.  To secure workloads communicating
   over other transports, new protocol bindings will need to be defined.
   We note though that this protocol is designed to allow some level of
   reuse.  In particular, we expect that the Workload Identity Token
   (WIT) construct will be reusable in other settings.  The Workload
   Proof Token (WPT) may be adaptable with some changes to different
   environments.

1.2.  Deployment Architecture and Message Flow

   Regardless of the transport between the workloads, we assume the
   following logical architecture (numbers refer to the sequence of
   steps listed below):













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   +------------+               +------------+
   |            |      (1)      |            |
   |            |<=============>|            |
   |            |               |            |
   | Workload A |      (3)      | Workload B |
   |            |==============>|            |
   |            |               |            |
   |            |      (5)      |   +--------+
   |            |<==============|   |  PEP   |
   +------------+               +---+--------+
         ^                        ^     ^
         |            (2)         |     |
     (2) | +----------------------+     | (4)
         | |                            |
         v v                            v
   +------------+               +------------+
   |            |               |            |
   |  Identity  |               |    PDP     |
   |   Server   |               | (optional) |
   |            |               |            |
   +------------+               +------------+

                      Figure 1: Sequence of Operations

   The Identity Server provisions credentials to each of the workloads.
   At least Workload A (and possibly both) must be provisioned with a
   credential before the call can proceed.  Details of communication
   with the Identity Server are out of scope of this document, however
   we do describe the credential received by the workload.

   PEP is a Policy Enforcement Point, the component that allows the call
   to go through or blocks it.  PDP is an optional Policy Decision
   Point, which may be deployed in architectures where policy management
   is centralized.  All details of policy management and message
   authorization are out of scope of this document.

   The high-level message flow is as follows:

   1.  A transport connection is set up.  In the case of mutual TLS,
       this includes authentication of both workloads to one another.
       In the case of application-level security, the TLS connection is
       typically one-way authenticated, and workload-level
       authentication does not yet take place.

   2.  Workload A (and similarly, Workload B) obtains a credential from
       the Identity Server.  This happens periodically, e.g. once every
       24 hours.




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   3.  Workload A makes an HTTP call into Workload B.  This is a regular
       HTTP request, with the additional protection mechanisms defined
       below.

   4.  In the case of application-level security, Workload B
       authenticates Workload A (when using mutual TLS, this happened in
       step 1).  In either case, Workload B decides whether to authorize
       the call.  In certain architectures, Workload B may need to
       consult with an external server when making this decision.

   5.  Workload B returns a response to Workload A, which may be an
       error response or a regular one.

1.3.  Workload Identifiers and Authentication Granularity

   The specific format of workload identifiers (see
   [I-D.ietf-wimse-arch]) is set by local policy for each deployment,
   and this choice has several implications.

   Prior to WIMSE, many use cases did not allow for fully granular
   authentication in containerized runtime platforms.  For instance,
   with mutual TLS, there's often no clear way to map the request's
   external access reference (e.g., Kubernetes Ingress path, service
   name, or host header) to the SubjectAltName value in the server
   certificate.  This means that the client could only verify if the
   server certificate is valid within a trust domain, not if it's tied
   to a specific workload.

   To enable mutual and granular authentication between workloads, two
   things must be in place:

   *  Each workload must know its own identifier.

   *  There needs to be an explicit mapping from the external handle
      used to access a workload (such as an Ingress path or service DNS
      name) to its workload identifier.

   Once these conditions are met, the methods described in this document
   can be used for the caller and callee to mutually authenticate.

   Implementations MUST allow for defining this mapping between the
   workload's access path and the workload identifier (e.g., through
   callback functions).  Deployments SHOULD use these features to
   establish a consistent set of identifiers within their environment.







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2.  Conventions and Definitions

   All terminology in this document follows [I-D.ietf-wimse-arch].

   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.  Application Level Workload To Workload Authentication

   As noted in the Introduction, for many deployments communication
   between workloads cannot use end-to-end TLS.  For these deployment
   styles, this document proposes application-level protections.

   The current version of the document includes two alternatives, both
   using the newly introduced Workload Identity Token (Section 3.1).
   The first alternative (Section 3.2) is inspired by the OAuth DPoP
   specification.  The second (Section 3.3) is based on the HTTP Message
   Signatures RFC.  We present both alternatives and expect the working
   group to select one of them as this document progresses towards IETF
   consensus.  A comparison of the two alternatives is attempted in
   Section 3.4.

3.1.  The Workload Identity Token

   The Workload Identity Token (WIT) is a JWS [RFC7515] signed JWT
   [RFC7519] that represents the identity of a workload.  It is issued
   by the Identity Server and binds a public key to the workload
   identity.  A WIT MUST contain the following claims, except where
   noted:

   *  in the JOSE header:

      -  alg: An identifier for a JWS asymmetric digital signature
         algorithm (registered algorithm identifiers are listed in the
         IANA JOSE Algorithms registry [IANA.JOSE.ALGS]).  The value
         none MUST NOT be used.

      -  typ: the WIT is explicitly typed, as recommended in
         Section 3.11 of [RFC8725], using the wimse-id+jwt media type.

   *  in the JWT claims:

      -  iss: The issuer of the token, which is the Identity Server,
         represented by a URI.  The iss claim is RECOMMENDED but
         optional, see Section 3.1.2 for more.



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      -  sub: The subject of the token, which is the identity of the
         workload, represented by a URI.  See [I-D.ietf-wimse-arch] for
         details of the Workload Identifier.  And see Section 1.3 for
         security implications of these identifiers.

      -  exp: The expiration time of the token (as defined in
         Section 4.1.4 of [RFC7519]).  WITs should be refreshed
         regularly, e.g. on the order of hours.

      -  jti: A unique identifier for the token.  This claim is
         OPTIONAL.  The jti claim is frequently useful for auditing
         issuance of individual WITs or to revoke them, but some token
         generation environments do not support it.

      -  cnf: A confirmation claim referencing the public key of the
         workload.

         o  jwk: Within the cnf claim, a jwk key MUST be present that
            contains the public key of the workload as defined in
            Section 3.2 of [RFC7800].  The workload MUST prove
            possession of the corresponding private key when presenting
            the WIT to another party, which can be accomplished by using
            it in conjunction with one of the methods in Section 3.2 or
            Section 3.3.  As such, it MUST NOT be used as a bearer token
            and is not intended for use in the Authorization header.

            +  alg: Within the jwk object, an alg field MUST be present.
               Allowed values are listed in the IANA "JSON Web Signature
               and Encryption Algorithms" registry established by
               [RFC7518].  The presented proof (WPT or http-sig) MUST be
               produced with the algorithm specified in this field.  The
               value none MUST NOT be used.  Algorithms used in
               combination with symmetric keys MUST NOT be used.  Also
               encryption algorithms MUST NOT be used as this would
               require additional key distribution outside of the WIT.
               To promote interoperability, the ES256 signing algorithm
               MUST be supported by general purpose implementations of
               this document.

   An example WIT might look like this:











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   =============== NOTE: '\' line wrapping per RFC 8792 ================

   eyJhbGciOiJFUzI1NiIsImtpZCI6Ikp1bmUgNSIsInR5cCI6IndpbXNlLWlkK2p3dCJ9\
   .eyJjbmYiOnsiandrIjp7ImFsZyI6IkVkRFNBIiwiY3J2IjoiRWQyNTUxOSIsImt0eSI\
   6Ik9LUCIsIngiOiIxQ1hYdmZsTl9MVlZzSXNZWHNVdkIwM0ptbEdXZUNIcVFWdW91Q0Y\
   5MmJnIn19LCJleHAiOjE3NDU1MTI1MTAsImlhdCI6MTc0NTUwODkxMCwianRpIjoiYmQ\
   yYTdiNWJmODU3M2E0MWFkYjRjYmYzY2ZhMDFlMTUiLCJzdWIiOiJ3aW1zZTovL2V4YW1\
   wbGUuY29tL3NwZWNpZmljLXdvcmtsb2FkIn0.xpODXCUhZ2zk-1-W3VEqbqWhBX6_OJI\
   l7vtjahgwJStMOCRn6J6is6f5mz-Pi5-Xk6FmV44k48NzulqMDVJbAw

             Figure 2: An example Workload Identity Token (WIT)

   The decoded JOSE header of the WIT from the example above is shown
   here:

   {
     "alg": "ES256",
     "kid": "June 5",
     "typ": "wimse-id+jwt"
   }

                     Figure 3: Example WIT JOSE Header

   The decoded JWT claims of the WIT from the example above are shown
   here:

   {
     "cnf": {
       "jwk": {
         "alg": "EdDSA",
         "crv": "Ed25519",
         "kty": "OKP",
         "x": "1CXXvflN_LVVsIsYXsUvB03JmlGWeCHqQVuouCF92bg"
       }
     },
     "exp": 1745512510,
     "iat": 1745508910,
     "jti": "bd2a7b5bf8573a41adb4cbf3cfa01e15",
     "sub": "wimse://example.com/specific-workload"
   }

                        Figure 4: Example WIT Claims

   The claims indicate that the example WIT:

   *  was issued by an Identity Server known as wimse://example.com/
      trusted-central-authority.




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   *  is valid until May 15, 2024 3:28:45 PM GMT-06:00 (represented as
      NumericDate Section 2 of [RFC7519] value 1717612470).

   *  identifies the workload to which the token was issued as
      wimse://example.com/specific-workload.

   *  has a unique identifier of x-_1CTL2cca3CSE4cwb__.

   *  binds the public key represented by the jwk confirmation method to
      the workload wimse://example.com/specific-workload.

   *  requires the proof to be produced with the EdDSA signature
      algorithm.

   For elucidative purposes only, the workload's key, including the
   private part, is shown below in JWK [RFC7517] format:

   {
    "kty": "OKP",
    "crv": "Ed25519",
    "x": "1CXXvflN_LVVsIsYXsUvB03JmlGWeCHqQVuouCF92bg",
    "d": "sdLX8yCYKqo_XvGBLn-ZWeKT7llYeeQpgeCaXVxb5kY"
   }

                      Figure 5: Example Workload's Key

   The afore-exampled WIT is signed with the private key of the Identity
   Server.  The public key(s) of the Identity Server need to be known to
   all workloads in order to verify the signature of the WIT.  The
   Identity Server's public key from this example is shown below in JWK
   [RFC7517] format:

   {
    "kty": "EC",
    "kid": "June 5",
    "crv": "P-256",
    "x": "Dy47KDeYao6kOhxSraJeJizjVxHjjo-9NsnrMqLyvOo",
    "y": "bj3s7bncoSYURzAzF0jBy0JOnnP5-5E11vx5QoYEFgk"
   }

                   Figure 6: Example Identity Server Key

3.1.1.  The WIT HTTP Header

   A WIT is conveyed in an HTTP header field named Workload-Identity-
   Token.





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   ABNF [RFC5234] for the value of Workload-Identity-Token header field
   is provided in Figure 7:

   ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
   DIGIT = %x30-39 ; 0-9
   base64url = 1*(ALPHA / DIGIT / "-" / "_")
   JWT =  base64url "." base64url "." base64url
   WIT =  JWT

            Figure 7: Workload-Identity-Token Header Field ABNF

   The following shows the WIT from Figure 2 in an example of a
   Workload-Identity-Token header field:

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   Workload-Identity-Token: eyJhbGciOiJFUzI1NiIsImtpZCI6Ikp1bmUgNSIsInR\
   5cCI6IndpbXNlLWlkK2p3dCJ9.eyJjbmYiOnsiandrIjp7ImFsZyI6IkVkRFNBIiwiY3\
   J2IjoiRWQyNTUxOSIsImt0eSI6Ik9LUCIsIngiOiIxQ1hYdmZsTl9MVlZzSXNZWHNVdk\
   IwM0ptbEdXZUNIcVFWdW91Q0Y5MmJnIn19LCJleHAiOjE3NDU1MTI1MTAsImlhdCI6MT\
   c0NTUwODkxMCwianRpIjoiYmQyYTdiNWJmODU3M2E0MWFkYjRjYmYzY2ZhMDFlMTUiLC\
   JzdWIiOiJ3aW1zZTovL2V4YW1wbGUuY29tL3NwZWNpZmljLXdvcmtsb2FkIn0.xpODXC\
   UhZ2zk-1-W3VEqbqWhBX6_OJIl7vtjahgwJStMOCRn6J6is6f5mz-Pi5-Xk6FmV44k48\
   NzulqMDVJbAw

       Figure 8: An example Workload Identity Token HTTP Header Field

   Note that per [RFC9110], header field names are case insensitive;
   thus, Workload-Identity-Token, workload-identity-token, WORKLOAD-
   IDENTITY-TOKEN, etc., are all valid and equivalent header field
   names.  However, case is significant in the header field value.

3.1.2.  A note on iss claim and key distribution

   It is RECOMMENDED that the WIT carries an iss claim.  This
   specification itself does not make use of a potential iss claim but
   also carries the trust domain in the workload identifier (see
   [I-D.ietf-wimse-arch] for a definition of the identifier and related
   rules).  Implementations MAY include the iss claim in the form of a
   https URL to facilitate key distribution via mechanisms like the
   jwks_uri from [RFC8414] but alternative key distribution methods may
   make use of the trust domain included in the workload identifier
   which is carried in the mandatory sub claim.








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3.2.  Option 1: DPoP-Inspired Authentication

   This option, inspired by the OAuth DPoP specification [RFC9449], uses
   a DPoP-like mechanism to authenticate the calling workload in the
   context of the request.  The Workload Identity Token (Section 3.1) is
   sent in the request as described in Section 3.1.1.  An additional
   JWT, the Workload Proof Token (WPT), is signed by the private key
   corresponding to the public key in the WIT.  The WPT is sent in the
   Workload-Proof-Token header field of the request.  The ABNF syntax of
   the Workload-Proof-Token header field is:

   WPT =  JWT

              Figure 9: Workload-Proof-Token Header Field ABNF

   where the JWT projection is defined in Figure 7.

   A WPT MUST contain the following:

   *  in the JOSE header:

      -  alg: An identifier for an appropriate JWS asymmetric digital
         signature algorithm corresponding to the confirmation key in
         the associated WIT.  The value MUST match the alg value of the
         jwk in the cnf claim of the WIT.  See Section 3.1 for valid
         values and restrictions.

      -  typ: the WPT is explicitly typed, as recommended in
         Section 3.11 of [RFC8725], using the application/wimse-
         proof+jwt media type.

   *  in the JWT claims:

      -  aud: The audience SHOULD contain the HTTP target URI
         (Section 7.1 of [RFC9110]) of the request to which the WPT is
         attached, without query or fragment parts.  However, there may
         be some normalization, rewriting or other process that requires
         the audience to be set to a deployment-specific value.  See
         also Section 1.3 for more details.

      -  exp: The expiration time of the WIT (as defined in
         Section 4.1.4 of [RFC7519]).  WPT lifetimes MUST be short,
         e.g., on the order of minutes or seconds.

      -  jti: An identifier for the token.  The value MUST be unique, at
         least within the scope of the sender.





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      -  wth: Hash of the Workload Identity Token, defined in
         Section 3.1.  The value is the base64url encoding of the
         SHA-256 hash of the ASCII encoding of the token's value.

      -  ath: Hash of the OAuth access token, if present in the request,
         which might convey end-user identity and authorization context
         of the request.  The value, as per Section 4.1 of [RFC9449], is
         the base64url encoding of the SHA-256 hash of the ASCII
         encoding of the access token's value.

      -  tth: Hash of the Txn-Token [I-D.ietf-oauth-transaction-tokens],
         if present in the request, which might convey end-user identity
         and authorization context of the request.  The value MUST be
         the result of a base64url encoding (as defined in Section 2 of
         [RFC7515]) of the SHA-256 hash of the ASCII encoding of the
         associated token's value.

      -  oth: Hash of any other token in the request that might convey
         end-user identity and authorization context of the request, if
         such a token exists.  The value MUST be the result of a
         base64url encoding (as defined in Section 2 of [RFC7515]) of
         the SHA-256 hash of the ASCII encoding of the associated
         token's value.  (Note: this is less than ideal but seems we
         need something like this for extensibility.)

   To clarify: the ath, tth and oth claims are each mandatory if the
   respective token is included in the request.

   An example WPT might look like the following:

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   eyJhbGciOiJFZERTQSIsInR5cCI6IndpbXNlLXByb29mK2p3dCJ9.eyJhdGgiOiJDTDR\
   3amZwUm1OZi1iZFlJYllMblY5ZDVyTUFSR3dLWUUxMHdVd3pDMGpJIiwiYXVkIjoiaHR\
   0cHM6Ly93b3JrbG9hZC5leGFtcGxlLmNvbS9wYXRoIiwiZXhwIjoxNzQ1NTA5MjEwLCJ\
   qdGkiOiJlMzI5YmI4Njk2YWE0YWVjYTA0ODg2ZGQ3NmU3OGIyNiIsInd0aCI6InJvN3h\
   GT1NHX2pZeG1VV2Z3ZXFrNVgxc2M2TDBzQ2o3NVdLVDkxZ014eFUifQ.oSegRTrBxuQN\
   55oyWRK5PnPEZLhgRy0Va7BpxBw-a64E3map15dbDo9ArRcJ8M4Z4QZ829CCppfnuaLI\
   ei1bBQ

               Figure 10: Example Workload Proof Token (WPT)

   The decoded JOSE header of the WPT from the example above is shown
   here:







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   {
     "alg": "EdDSA",
     "typ": "wimse-proof+jwt"
   }

                     Figure 11: Example WPT JOSE Header

   The decoded JWT claims of the WPT from the example above are shown
   here:

   {
     "ath": "CL4wjfpRmNf-bdYIbYLnV9d5rMARGwKYE10wUwzC0jI",
     "aud": "https://workload.example.com/path",
     "exp": 1740755048,
     "jti": "0c740386ca1dcad37de1b5f9de1b0705",
     "wth": "aA0W_oFJK7qV7zYhcmzR1KOXVCHjd2x6c4sOQLvE90Y"
   }

                       Figure 12: Example WPT Claims

   An example of an HTTP request with both the WIT and WPT from prior
   examples is shown below:

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   POST /path HTTP/1.1
   Host: workload.example.com
   Content-Type: application/json
   Authorization: Bearer 16_mAd0GiwaZokU26_0902100
   Workload-Identity-Token: eyJhbGciOiJFUzI1NiIsImtpZCI6Ikp1bmUgNSIsInR\
   5cCI6IndpbXNlLWlkK2p3dCJ9.eyJjbmYiOnsiandrIjp7ImNydiI6IkVkMjU1MTkiLC\
   JrdHkiOiJPS1AiLCJ4Ijoiclp3VUEwVHJIazRBWEs5MkY2Vll2bUhIWDN4VU0tSUdsck\
   11VkNRaG04VSJ9fSwiZXhwIjoxNzQwNzU4MzQ4LCJpYXQiOjE3NDA3NTQ3NDgsImp0aS\
   I6IjRmYzc3ZmNlZjU3MWIzYmIzM2I2NzJlYWYyMDRmYWY0Iiwic3ViIjoid2ltc2U6Ly\
   9leGFtcGxlLmNvbS9zcGVjaWZpYy13b3JrbG9hZCJ9.j-WlF3bufTwWeVZQntPhlzvST\
   Pwf37-4wfazJZARdHYmW9S_olB5nKEqwqTZpIX_LoVVIcyK0VBE7Fa0CMvw2g
   Workload-Proof-Token: eyJhbGciOiJFZERTQSIsInR5cCI6IndpbXNlLXByb29mK2\
   p3dCJ9.eyJhdGgiOiJDTDR3amZwUm1OZi1iZFlJYllMblY5ZDVyTUFSR3dLWUUxMHdVd\
   3pDMGpJIiwiYXVkIjoiaHR0cHM6Ly93b3JrbG9hZC5leGFtcGxlLmNvbS9wYXRoIiwiZ\
   XhwIjoxNzQwNzU1MDQ4LCJqdGkiOiIwYzc0MDM4NmNhMWRjYWQzN2RlMWI1ZjlkZTFiM\
   DcwNSIsInd0aCI6ImFBMFdfb0ZKSzdxVjd6WWhjbXpSMUtPWFZDSGpkMng2YzRzT1FMd\
   kU5MFkifQ.W9RZqieXeD-UgdtbYf8ZNkf2_6_6b_kJSfkODQdq3_QDSSGOhVbRAR3qQo\
   Ou0SzihiG6HCsGwslfo4WdvnH5AQ

   {"do stuff":"please"}

              Figure 13: Example HTTP Request with WIT and WPT




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   To validate the WPT in the request, the recipient MUST ensure the
   following:

   *  There is exactly one Workload-Proof-Token header field in the
      request.

   *  The Workload-Proof-Token header field value is a single and well-
      formed JWT.

   *  The signature algorithm in the alg JOSE header string-equal
      matches the alg attribute of the jwk in the cnf claim of the WIT.

   *  The WPT signature is valid using the public key from the
      confirmation claim of the WIT.

   *  The typ JOSE header parameter of the WPT conveys a media type of
      wimse-proof+jwt.

   *  The aud claim of the WPT matches the target URI, or an acceptable
      alias or normalization thereof, of the HTTP request in which the
      WPT was received, ignoring any query and fragment parts.  See also
      Section 1.3 for implementation advice on this verification check.

   *  The exp claim is present and conveys a time that has not passed.
      WPTs with an expiration time unreasonably far in the future SHOULD
      be rejected.

   *  The wth claim is present and matches the hash of the token value
      conveyed in the Workload-Identity-Token header.

   *  It is RECOMMENDED to check that the value of the jti claim has not
      been used before in the time window in which the respective WPT
      would be considered valid.

   *  If presented in conjunction with an OAuth access token, the value
      of the ath claim matches the hash of that token's value.

   *  If presented in conjunction with a Txn-Token, the value of the tth
      claim matches the hash of that token's value.

   *  If presented in conjunction with a token conveying end-user
      identity or authorization context, the value of the oth claim
      matches the hash of that token's value.








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3.3.  Option 2: Authentication Based on HTTP Message Signatures

   This option uses the Workload Identity Token (Section 3.1) to sign
   the request and optionally, the response.  This section defines a
   profile of the Message Signatures specification [RFC9421].

   The request is signed as per [RFC9421].  The following derived
   components MUST be signed:

   *  @method

   *  @request-target

   In addition, the following request headers MUST be signed when they
   exist:

   *  Content-Type

   *  Content-Digest

   *  Authorization

   *  Txn-Token [I-D.ietf-oauth-transaction-tokens]

   *  Workload-Identity-Token

   If the response is signed, the following components MUST be signed:

   *  @status

   *  @method;req

   *  @request-target;req

   *  Content-Type if it exists

   *  Content-Digest if it exists

   *  Workload-Identity-Token

   To ensure the message is fully integrity-protected, if the request or
   response includes a message body, the sender MUST include (and the
   receiver MUST verify) a Content-Digest header.

   For both requests and responses, the following signature parameters
   MUST be included:

   *  created



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   *  expires - expiration MUST be short, e.g. on the order of minutes.
      The WIMSE architecture will provide separate mechanisms in support
      of long-lived compute processes.

   *  nonce

   *  tag - the value for implementations of this specification is
      wimse-workload-to-workload

   The following signature parameters in the Signature-Input header MUST
   NOT be used:

   *  keyid - The signing key is sent along with the message in the WIT.
      Additionally specifying the key identity would add confusion.

   *  alg - The signature algorithm is specified in the jwk section of
      the cnf claim in the WIT.  See Section 3.1 and Sec. 3.3.7 of
      [RFC9421] for details.

   It is RECOMMENDED to include only one signature with the HTTP
   message.  If multiple ones are included, then the signature label
   included in both the Signature-Input and Signature headers SHOULD be
   wimse.

   A sender MUST ensure that each nonce it generates is unique, at least
   among messages sent to the same recipient.  To detect message
   replays, a recipient SHOULD reject a message (request or response) if
   a nonce generated by a certain peer is seen more than once.

   Following is a non-normative example of a signed request and a signed
   response, where the caller is using the keys specified in Figure 5.

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   GET /gimme-ice-cream?flavor=vanilla HTTP/1.1
   Host: example.com
   Signature: wimse=:K4dfGnguF5f1L4DKBSp5XeFXosLGj8Y9fiUX06rL/wdOF+x3zT\
   WmsvKWiY0B1oFZaOtm2FHru+YLjdkqa2WfCQ==:
   Signature-Input: wimse=("@method" "@request-target" "workload-identi\
   ty-token");created=1718291357;expires=1718291657;nonce="abcd1111";ta\
   g="wimse-workload-to-workload"
   Workload-Identity-Token: aGVhZGVyCg.VGhpcyBpcyBub3QgYSByZWFsIHRva2Vu\
   Lgo.c2lnbmF0dXJlCg

                         Figure 14: Signed Request

   Assuming that the workload being called has the following keypair:




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   {
    "kty":"OKP",
    "crv":"Ed25519",
    "x":"CfaY1XX-aHJpenRP8ATm3yGlbcKA_treqOfwKrilwyg",
    "d":"fycSKS-iHZ6TC1BNwN6cE0sOBP3-4KgR-eqxNpnyhws"
   }

                       Figure 15: Callee Private Key

   A signed response would be:

   =============== NOTE: '\' line wrapping per RFC 8792 ================

   HTTP/1.1 404 Not Found
   Connection: close
   Content-Digest: sha-256=:47DEQpj8HBSa+/TImW+5JCeuQeRkm5NMpJWZG3hSuFU\
   =:
   Content-Type: text/plain
   Signature: wimse=:NMrMn3xhI6m9PI8mKVfpnH5qFGcEfuFxiCmsB5PJhGjUHT/5J4\
   612EZwRw3V4kU4gGJmO+ER8RC4DM2HKVOYDQ==:
   Signature-Input: wimse=("@status" "workload-identity-token" "content\
   -type" "content-digest" "@method";req "@request-target";req);created\
   =1718295368;expires=1718295670;nonce="abcd2222";tag="wimse-workload-\
   to-workload"
   Workload-Identity-Token: aGVhZGVyCg.VGhpcyBhaW4ndCBvbmUsIHRvby4K.c2l\
   nbmF0dXJlCg

   No ice cream today.

                         Figure 16: Signed Response

3.4.  Comparing the DPoP Inspired Option with Message Signatures

   The two workload protection options have different strengths and
   weaknesses regarding implementation complexity, extensibility, and
   security.  Here is a summary of the main differences between
   Section 3.2 and Section 3.3.

   *  The DPoP-inspired solution is less HTTP-specific, making it easier
      to adapt for other protocols beyond HTTP.  This flexibility is
      particularly valuable for asynchronous communication scenarios,
      such as event-driven systems.

   *  Message Signatures, on the other hand, benefit from an existing
      HTTP-specific RFC with some established implementations.  This
      existing groundwork means that this option could be simpler to
      deploy, to the extent such implementations are available and
      easily integrated.



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   *  Given that the WIT (Workload Identity Token) is a type of JWT, the
      DPoP-inspired approach that also uses JWT is less complex and
      technology-intensive than Message Signatures.  In contrast,
      Message Signatures introduce an additional layer of technology,
      potentially increasing the complexity of the overall system.

   *  Message Signatures offer superior integrity protection,
      particularly by mitigating message modification by middleboxes.
      See also Section 5.3.

   *  A key advantage of Message Signatures is that they support
      response signing.  This opens up the possibility for future
      decisions about whether to make response signing mandatory,
      allowing for flexibility in the specification and/or in specific
      deployment scenarios.

   *  In general, Message Signatures provide greater flexibility
      compared to the DPoP-inspired approach.  Future versions of this
      draft (and subsequent implementations) can decide whether specific
      aspects of message signing, such as coverage of particular fields,
      should be mandatory or optional.  Covering more fields will
      constrain the proof so it cannot be easily reused in another
      context, which is often a security improvement.  The DPoP inspired
      approach could be designed to include extensibility to sign other
      fields, but this would make it closer to trying to reinvent
      Message Signatures.

3.5.  Error Conditions

   Errors may occur during the processing of the message signature or
   WPT.  If the signature verification fails for any reason, such as an
   invalid signature, an expired validity time window, or a malformed
   data structure, an error is returned.  Typically, this will be in
   response to an API call, so an HTTP status code such as 400 (Bad
   Request) is appropriate.  This response could include more details as
   per [RFC9457], such as an indicator that the wrong key material or
   algorithm was used.

3.6.  Coexistence with JWT Bearer Tokens

   The WIT and WPT define new HTTP headers.  They can therefore be
   presented along with existing headers used for JWT bearer tokens.
   This property allows for transition from mechanisms using identity
   tokens based on bearer JWTs to proof of possession based WITs.  A
   workload may implement a policy that accepts both bearer tokens and
   WITs during a transition period.  This policy may be configurable
   per-caller to allow the workload to reject bearer tokens from callers
   that support WITs.  Once a deployment fully supports WITs, then the



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   use of bearer tokens for identity can be disabled through policy.
   Implementations should be careful when implementing such a transition
   strategy, since the decision which token to prefer is made when the
   caller's identity has still not been authenticated, and needs to be
   revalidated following the authentication step.

   The WIT can also coexist with tokens used to establish security
   context, such as transaction tokens
   [I-D.ietf-oauth-transaction-tokens].  In this case a workload's
   authorization policy may take into account both the sending
   workload's identity and the information in the context token.  For
   example, the identity in the WIT may be used to establish which API
   calls can be made and information in the context token may be used to
   determine which specific resources can be accessed.

4.  Using Mutual TLS for Workload To Workload Authentication

   As noted in the introduction, for many deployments, transport-level
   protection of application traffic using TLS is ideal.

4.1.  The Workload Identity Certificate

   The Workload Identity Certificate is an X.509 certificate.  The
   workload identity MUST be encoded in a SubjectAltName extension of
   type URI.  There MUST be only one SubjectAltName extension of type
   URI in a workload certificate.  If the workload will act as a TLS
   server for clients that do not understand workload identities it is
   RECOMMENDED that the workload certificate contain a SubjectAltName of
   type DNSName with the appropriate DNS names for the server.  The
   certificate MAY contain SubjectAltName extensions of other types.

4.2.  Workload Identity Certificate Validation

   Workload certificates may be used to authenticate both the server and
   client side of the connections.  When validating a workload
   certificate, the relying party MUST use the trust anchors configured
   for the trust domain in the workload identity to validate the peer's
   certificate.  Other PKIX [RFC5280] path validation rules apply.
   WIMSE clients and servers MUST validate that the trust domain portion
   of the workload certificate matches the expected trust domain for the
   other side of the connection.

   Servers wishing to use the workload certificate for authorizing the
   client MUST require client certificate authentication in the TLS
   handshake.  Other methods of post handshake authentication are not
   specified by this document.





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   WIMSE server certificates SHOULD have the id-kp-serverAuth extended
   key usage [RFC5280] field set and WIMSE client certificates SHOULD
   have the id-kp-clientAuth extended key usage field set.  A
   certificate that is used for both client and server connections may
   have both fields set.  This specification does not make any other
   requirements beyond [RFC5280] on the contents of workload
   certificates or on the certification authorities that issue workload
   certificates.

4.2.1.  Server Name Validation

   If the WIMSE client uses a hostname to connect to the server and the
   server certificate contain a DNS SAN the client MUST perform standard
   host name validation (Section 6.3 of [RFC9525]) unless it is
   configured with the information necessary to validate the peer's
   workload identity.  If the client did not perform standard host name
   validation then the WIMSE client SHOULD further use the workload
   identifier to validate the server.  The host portion of the workload
   identifier is NOT treated as a host name as specified in section 6.4
   of [RFC9525] but rather as a trust domain.  The server identity is
   encoded in the path portion of the workload identifier in a
   deployment specific way.  Validating the workload identity could be a
   simple match on the trust domain and path portions of the identifier
   or validation may be based on the specific details on how the
   identifier is constructed.  The path portion of the WIMSE identifier
   MUST always be considered in the scope of the trust domain.  In most
   cases it is preferable to validate the entire workload identifier,
   see Section 1.3 for additional implementation advice.

4.3.  Client Authorization Using the Workload Identity

   The server application retrieves the workload identifier from the
   client certificate subjectAltName, which in turn is obtained from the
   TLS layer.  The identifier is used in authorization, accounting and
   auditing.  For example, the full workload identifier may be matched
   against ACLs to authorize actions requested by the peer and the
   identifier may be included in log messages to associate actions to
   the client workload for audit purposes.  A deployment may specify
   other authorization policies based on the specific details of how the
   workload identifier is constructed.  The path portion of the workload
   identifier MUST always be considered in the scope of the trust
   domain.  See Section 1.3 on additional security implications of
   workload identifiers.

5.  Security Considerations






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5.1.  Workload Identity

   The Workload Identifier is scoped within an issuer and therefore any
   sub-components (path portion of Identifier) are only unique within a
   trust domain defined by the issuer.  Using a Workload Identifier
   without taking into account the trust domain could allow one domain
   to issue tokens to spoof identities in another domain.  Additionally,
   the trust domain must be tied to an authorized issuer cryptographic
   trust anchor through some mechanism such as a JWKS or X.509
   certificate chain.  The association of an issuer, trust domain and a
   cryptographic trust anchor MUST be communicated securely out of band.

5.2.  Workload Identity Token and Proof of Possession

   The Workload Identity Token (WIT) is bound to a secret cryptographic
   key and is always presented with a proof of possession as described
   in Section 3.1.  The WIT is a general purpose token that can be
   presented in multiple contexts.  The WIT and its PoP are only used in
   the application-level options, and both are not used in MTLS.  The
   WIT MUST NOT be used as a bearer token.  While this helps reduce the
   sensitivity of the token it is still possible that a token and its
   proof of possession may be captured and replayed within the PoP's
   lifetime.  The following are some mitigations for the capture and
   reuse of the proof of possession (PoP):

   *  Preventing Eavesdropping and Interception with TLS

   An attacker observing or intercepting the communication channel can
   view the token and its proof of possession and attempt to replay it
   to gain an advantage.  In order to prevent this the token and proof
   of possession MUST be sent over a secure, server authenticated TLS
   connection unless a secure channel is provided by some other
   mechanisms.  Host name validation according to Section 4.2.1 MUST be
   performed.  The WIT itself is not usable without a proof of
   possession.

   *  Limiting Proof of Possession Lifespan

   The proof of possession MUST be time limited.  A PoP should only be
   valid over the time necessary for it to be successfully used for the
   purpose it is needed.  This will typically be on the order of
   minutes.  PoPs received outside their validity time MUST be rejected.

   *  Limiting Proof of Possession Scope

   In order to reduce the risk of theft and replay the PoP should have a
   limited scope.  For example, a PoP may be targeted for use with a
   specific workload and even a specific transaction to reduce the



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   impact of a stolen PoP.  In some cases a workload may wish to reuse a
   PoP for a period of time or have it accepted by multiple target
   workloads.  A careful analysis is warranted to understand the impacts
   to the system if a PoP is disclosed allowing it to be presented by an
   attacker along with a captured WIT.

   *  Replay Protection

   A proof of possession includes the jti claim that MUST uniquely
   identify it, within the scope of a particular sender.  This claim
   SHOULD be used by the receiver to perform basic replay protection
   against tokens it has already seen.  Depending upon the design of the
   system it may be difficult to synchronize the replay cache across all
   token validators.  If an attacker can somehow influence the identity
   of the validator (e.g. which cluster member receives the message)
   then replay protection would not be effective.

   *  Binding to TLS Endpoint

   The POP MAY be bound to a transport layer sender such as the client
   identity of a TLS session or TLS channel binding parameters.  The
   mechanisms for binding are outside the scope of this specification.

5.3.  Middle Boxes

   In some deployments the Workload Identity Token and proof of
   possession may pass through multiple systems.  The communication
   between the systems is over TLS, but the token and PoP are available
   in the clear at each intermediary.  While the intermediary cannot
   modify the token or the information within the PoP they can attempt
   to capture and replay the token or modify the data not protected by
   the PoP.  Mitigations listed in the previous section can be used to
   provide some protection from middle boxes.  Deployments should
   perform analysis on their situation to determine if it is appropriate
   to trust and allow traffic to pass through a middle box.

5.4.  Privacy Considerations

   WITs and the proofs of possession may contain private information
   such as user names or other identities.  Care should be taken to
   prevent the disclosure of this information.  The use of TLS helps
   protect the privacy of WITs and proofs of possession.

   WITs and certificates with workload identifiers are typically
   associated with a workload and not a specific user, however in some
   deployments the workload may be associated directly to a user.  While
   these are exceptional cases a deployment should evaluate if the
   disclosure of WITs or certificates can be used to track a user.



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6.  IANA Considerations

6.1.  JSON Web Token Claims

   IANA is requested to add the following entries to the "JSON Web Token
   Claims" registry [IANA.JWT.CLAIMS]:

   +============+===================+===================+=============+
   | Claim Name | Claim Description | Change Controller | Reference   |
   +============+===================+===================+=============+
   | tth        | Transaction Token | IESG              | RFC XXX,    |
   |            | hash              |                   | Section 3.2 |
   +------------+-------------------+-------------------+-------------+
   | wth        | Workload Identity | IESG              | RFC XXX,    |
   |            | Token hash        |                   | Section 3.2 |
   +------------+-------------------+-------------------+-------------+
   | oth        | Other Token hash  | IESG              | RFC XXX,    |
   |            |                   |                   | Section 3.2 |
   +------------+-------------------+-------------------+-------------+

                                 Table 1

6.2.  Media Type Registration

   IANA is requested to register the following entries to the "Media
   Types" registry [IANA.MEDIA.TYPES]:

   *  application/wimse-id+jwt, per Section 6.2.1.

   *  application/wimse-proof+jwt, per Section 6.2.2.

6.2.1.  application/wimse-id+jwt

   Type name: application

   Subtype name: wimse-id+jwt

   Required parameters: N/A

   Optional parameters: N/A

   Encoding considerations: Encoding considerations are identical to
   those specified for the "application/jwt" media type.  See [RFC7519].

   Security considerations: See the Security Considerations section of
   RFC XXX.

   Interoperability considerations: N/A



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   Published specification: RFC XXX, Section 3.1.

   Applications that use this media type: Identity servers that vend
   Workload Identity Tokens, and Workloads that use these tokens to
   authenticate to each other.

   Fragment identifier considerations: N/A

   Additional information:

   Deprecated alias names for this type: N/A

   Magic number(s): N/A

   File extension(s): None

   Macintosh file type code(s): N/A

   Person & email address to contact for further information:

   See the Authors' Addresses section of RFC XXX.

   Intended usage: COMMON

   Restrictions on usage: N/A

   Author: See the Authors' Addresses section of RFC XXX.

   Change controller: Internet Engineering Task Force (iesg@ietf.org).

6.2.2.  application/wimse-proof+jwt

   Type name: application

   Subtype name: wimse-proof+jwt

   Required parameters: N/A

   Optional parameters: N/A

   Encoding considerations: Encoding considerations are identical to
   those specified for the "application/jwt" media type.  See [RFC7519].

   Security considerations: See the Security Considerations section of
   RFC XXX.

   Interoperability considerations: N/A




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   Published specification: RFC XXX, Section 3.2.

   Applications that use this media type: Workloads that use these
   tokens to integrity-protect messages in the WIMSE workload-to-
   workload protocol.

   Fragment identifier considerations: N/A

   Additional information:

   Deprecated alias names for this type: N/A

   Magic number(s): N/A

   File extension(s): None

   Macintosh file type code(s): N/A

   Person & email address to contact for further information:

   See the Authors' Addresses section of RFC XXX.

   Intended usage: COMMON

   Restrictions on usage: N/A

   Author: See the Authors' Addresses section of RFC XXX.

   Change controller: Internet Engineering Task Force (iesg@ietf.org).

6.3.  Hypertext Transfer Protocol (HTTP) Field Name Registration

   IANA is requested to register the following entries to the "Hypertext
   Transfer Protocol (HTTP) Field Name Registry" [IANA.HTTP.FIELDS]:

   *  Workload-Identity-Token, per Section 6.3.1.

   *  Workload-Proof-Token, per Section 6.3.2.

6.3.1.  Workload-Identity-Token

   *  Field Name: Workload-Identity-Token

   *  Status: permanent

   *  Structured Type: N/A

   *  Specification Document: RFC XXX, Section 3.1.1



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   *  Comments: see reference above for an ABNF syntax of this field

6.3.2.  Workload-Proof-Token

   *  Field Name: Workload-Proof-Token

   *  Status: permanent

   *  Structured Type: N/A

   *  Specification Document: RFC XXX, Section 3.2

   *  Comments: see reference above for an ABNF syntax of this field

7.  References

7.1.  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>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/rfc/rfc5234>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/rfc/rfc5280>.

   [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>.

   [RFC7517]  Jones, M., "JSON Web Key (JWK)", RFC 7517,
              DOI 10.17487/RFC7517, May 2015,
              <https://www.rfc-editor.org/rfc/rfc7517>.

   [RFC7518]  Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
              DOI 10.17487/RFC7518, May 2015,
              <https://www.rfc-editor.org/rfc/rfc7518>.






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   [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>.

   [RFC7800]  Jones, M., Bradley, J., and H. Tschofenig, "Proof-of-
              Possession Key Semantics for JSON Web Tokens (JWTs)",
              RFC 7800, DOI 10.17487/RFC7800, April 2016,
              <https://www.rfc-editor.org/rfc/rfc7800>.

   [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>.

   [RFC8414]  Jones, M., Sakimura, N., and J. Bradley, "OAuth 2.0
              Authorization Server Metadata", RFC 8414,
              DOI 10.17487/RFC8414, June 2018,
              <https://www.rfc-editor.org/rfc/rfc8414>.

   [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>.

   [RFC9110]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "HTTP Semantics", STD 97, RFC 9110,
              DOI 10.17487/RFC9110, June 2022,
              <https://www.rfc-editor.org/rfc/rfc9110>.

   [RFC9421]  Backman, A., Ed., Richer, J., Ed., and M. Sporny, "HTTP
              Message Signatures", RFC 9421, DOI 10.17487/RFC9421,
              February 2024, <https://www.rfc-editor.org/rfc/rfc9421>.

   [RFC9525]  Saint-Andre, P. and R. Salz, "Service Identity in TLS",
              RFC 9525, DOI 10.17487/RFC9525, November 2023,
              <https://www.rfc-editor.org/rfc/rfc9525>.

7.2.  Informative References

   [I-D.ietf-oauth-transaction-tokens]
              Tulshibagwale, A., Fletcher, G., and P. Kasselman,
              "Transaction Tokens", Work in Progress, Internet-Draft,
              draft-ietf-oauth-transaction-tokens-05, 3 March 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-oauth-
              transaction-tokens-05>.

   [I-D.ietf-wimse-arch]
              Salowey, J. A., Rosomakho, Y., and H. Tschofenig,
              "Workload Identity in a Multi System Environment (WIMSE)



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              Architecture", Work in Progress, Internet-Draft, draft-
              ietf-wimse-arch-04, 2 March 2025,
              <https://datatracker.ietf.org/doc/html/draft-ietf-wimse-
              arch-04>.

   [IANA.HTTP.FIELDS]
              IANA, "Hypertext Transfer Protocol (HTTP) Field Name
              Registry", <https://www.iana.org/assignments/http-fields>.

   [IANA.JOSE.ALGS]
              IANA, "JSON Web Signature and Encryption Algorithms",
              <https://www.iana.org/assignments/jose>.

   [IANA.JWT.CLAIMS]
              IANA, "JSON Web Token Claims",
              <https://www.iana.org/assignments/jwt>.

   [IANA.MEDIA.TYPES]
              IANA, "Media Types",
              <https://www.iana.org/assignments/media-types>.

   [RFC9449]  Fett, D., Campbell, B., Bradley, J., Lodderstedt, T.,
              Jones, M., and D. Waite, "OAuth 2.0 Demonstrating Proof of
              Possession (DPoP)", RFC 9449, DOI 10.17487/RFC9449,
              September 2023, <https://www.rfc-editor.org/rfc/rfc9449>.

   [RFC9457]  Nottingham, M., Wilde, E., and S. Dalal, "Problem Details
              for HTTP APIs", RFC 9457, DOI 10.17487/RFC9457, July 2023,
              <https://www.rfc-editor.org/rfc/rfc9457>.

Appendix A.  Document History


   // RFC Editor: please remove before publication.

A.1.  draft-ietf-wimse-s2s-protocol-06

   *  Explicit definition of the Workload Identity Certificate.

   *  Definition of the validation of workload identifiers as part of
      workload authentication.  Still work in progress.

A.2.  draft-ietf-wimse-s2s-protocol-05

   *  Removed the entire Workload Identity section which is now covered
      in the Architecture document.

   *  Content-Digest is mandatory with HTTP-Sig.



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   *  Some wording on extending the protocol beyond HTTP.

   *  IANA considerations.

A.3.  draft-ietf-wimse-s2s-protocol-04

   *  Require cnf.jwk.alg in WIT which restricts signature algorithm of
      WPT or HTTP-Sig.

   *  Replay protection as a SHOULD for both WPT and HTTP-Sig.

   *  Consolidate terminology with the Architecture draft.

A.4.  draft-ietf-wimse-s2s-protocol-03

   *  Consistently use "workload".

   *  Implement comments from the SPIFFE community.

   *  Make iss claim in WIT optional and add wording about its relation
      to key distribution.

   *  Remove iss claim from WPT.

   *  Make jti claim in WIT optional.

   *  Error handling for the application level methods.

A.5.  draft-ietf-wimse-s2s-protocol-02

   *  Coexistence with bearer tokens.

   *  Improve the architecture diagram.

   *  Some more ABNF.

   *  Clarified identifiers and URIs.

   *  Moved an author to acknowledgments.

A.6.  draft-ietf-wimse-s2s-protocol-01

   *  Addressed multiple comments from Pieter.

   *  Clarified WIMSE identity concepts, specifically "trust domain" and
      "workload identifier".

   *  Much more detail around mTLS, including some normative language.



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   *  WIT (the identity token) is now included in the WPT proof of
      possession.

   *  Added a section comparing the DPoP-inspired app-level security
      option to the Message Signature-based alternative.

A.7.  draft-ietf-wimse-s2s-protocol-00

   *  Initial WG draft, an exact copy of draft-sheffer-wimse-s2s-
      protocol-00

   *  Added this document history section

Acknowledgments

   The authors would like to thank Pieter Kasselman for his detailed
   comments.

   We thank Daniel Feldman for his contributions to earlier versions of
   this document.

Authors' Addresses

   Brian Campbell
   Ping Identity
   Email: bcampbell@pingidentity.com


   Joe Salowey
   CyberArk
   Email: joe@salowey.net


   Arndt Schwenkschuster
   SPIRL
   Email: arndts.ietf@gmail.com


   Yaron Sheffer
   Intuit
   Email: yaronf.ietf@gmail.com










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