ietf-wimse-ect/draft-nennemann-wimse-ect-00.md

---
title: "Execution Context Tokens for Distributed Agentic Workflows"
abbrev: "WIMSE Execution Context"
category: std
docname: draft-nennemann-wimse-ect-00
submissiontype: IETF
number:
date:
v: 3
area: "ART"
workgroup: "WIMSE"
keyword:
  - execution context
  - workload identity
  - agentic workflows
  - audit trail

author:
  -
    fullname: Christian Nennemann
    organization: Independent Researcher
    email: ietf@nennemann.de

normative:
  RFC7515:
  RFC7517:
  RFC7519:
  RFC7518:
  RFC9562:
  RFC9110:
  I-D.ietf-wimse-arch:
  I-D.ietf-wimse-s2s-protocol:

informative:
  RFC8693:
  SPIFFE:
    title: "Secure Production Identity Framework for Everyone (SPIFFE)"
    target: https://spiffe.io/docs/latest/spiffe-about/overview/
    date: false
  OPENTELEMETRY:
    title: "OpenTelemetry Specification"
    target: https://opentelemetry.io/docs/specs/otel/
    date: false
    author:
      - org: Cloud Native Computing Foundation
  I-D.ietf-scitt-architecture:
  RFC9449:
  I-D.ietf-oauth-transaction-tokens:
  I-D.oauth-transaction-tokens-for-agents:

--- abstract

This document defines Execution Context Tokens (ECTs), a JWT-based
extension to the WIMSE architecture that records task execution
across distributed agentic workflows.  Each ECT is a signed record
of a single task, linked to predecessor tasks through a directed
acyclic graph (DAG).  ECTs reuse the WIMSE signing model and are
transported in a new Execution-Context HTTP header field alongside
existing WIMSE identity headers.

--- middle

# Introduction

The WIMSE framework {{I-D.ietf-wimse-arch}} and its service-to-
service protocol {{I-D.ietf-wimse-s2s-protocol}} authenticate
workloads across call chains but do not record what those
workloads actually did.  This document defines Execution Context
Tokens (ECTs), a JWT-based extension that fills the gap between
workload identity and execution accountability.  Each ECT is a
signed record of a single task, linked to predecessor tasks
through a directed acyclic graph (DAG).

## Scope and Applicability

This document defines:

- The Execution Context Token (ECT) format ({{ect-format}})
- DAG structure for task dependency ordering ({{dag-validation}})
- An HTTP header for ECT transport ({{http-header}})
- Audit ledger interface requirements ({{ledger-interface}})

The following are out of scope and are handled by WIMSE:

- Workload authentication and identity provisioning
- Key distribution and management
- Trust domain establishment and management
- Credential lifecycle management

# Conventions and Definitions

{::boilerplate bcp14-tagged}

The following terms are used in this document:

Agent:
: An autonomous workload, as defined by WIMSE
  {{I-D.ietf-wimse-arch}}, that executes tasks within a workflow.

Task:
: A discrete unit of agent work that consumes inputs and produces
  outputs.

Directed Acyclic Graph (DAG):
: A graph structure representing task dependency ordering where
  edges are directed and no cycles exist.

Execution Context Token (ECT):
: A JSON Web Token {{RFC7519}} defined by this specification that
  records task execution details.

Audit Ledger:
: An append-only, immutable log of all ECTs within a workflow or
  set of workflows, used for audit and verification.

Workload Identity Token (WIT):
: A WIMSE credential proving a workload's identity within a trust
  domain.

Workload Proof Token (WPT):
: A WIMSE proof-of-possession token used for request-level
  authentication.

Trust Domain:
: A WIMSE concept representing an organizational boundary with a
  shared identity issuer, corresponding to a SPIFFE {{SPIFFE}}
  trust domain.

# Execution Context Token Format {#ect-format}

An Execution Context Token is a JSON Web Token (JWT) {{RFC7519}}
signed as a JSON Web Signature (JWS) {{RFC7515}}.  ECTs MUST use
JWS Compact Serialization (the base64url-encoded
`header.payload.signature` format) so that they can be carried in
a single HTTP header value.

ECTs reuse the WIMSE signing model.  The ECT MUST be signed with
the same private key associated with the agent's WIT.  The JOSE
header "kid" parameter MUST reference the public key identifier
from the agent's WIT, and the "alg" parameter MUST match the
algorithm used in the corresponding WIT.  In WIMSE deployments,
the ECT "iss" claim SHOULD use the WIMSE workload identifier
format (a SPIFFE ID {{SPIFFE}}).

## JOSE Header {#jose-header}

The ECT JOSE header MUST contain the following parameters:

~~~json
{
  "alg": "ES256",
  "typ": "wimse-exec+jwt",
  "kid": "agent-a-key-id-123"
}
~~~
{: #fig-header title="ECT JOSE Header Example"}

alg:
: REQUIRED.  The digital signature algorithm used to sign the ECT.
  MUST match the algorithm in the corresponding WIT.
  Implementations MUST support ES256 {{RFC7518}}.  The "alg"
  value MUST NOT be "none".  Symmetric algorithms (e.g., HS256,
  HS384, HS512) MUST NOT be used, as ECTs require asymmetric
  signatures for non-repudiation.

typ:
: REQUIRED.  MUST be set to "wimse-exec+jwt" to distinguish ECTs
  from other JWT types, consistent with the WIMSE convention for
  type parameter values.

kid:
: REQUIRED.  The key identifier referencing the public key from
  the agent's WIT {{RFC7517}}.  Used by verifiers to look up the
  correct public key for signature verification.

## JWT Claims {#jwt-claims}

### Standard JWT Claims

An ECT MUST contain the following standard JWT claims {{RFC7519}}:

iss:
: REQUIRED.  StringOrURI.  A URI identifying the issuer of the
  ECT.  In WIMSE deployments, this SHOULD be the workload's
  SPIFFE ID in the format `spiffe://<trust-domain>/<path>`,
  matching the "sub" claim of the agent's WIT.  Non-WIMSE
  deployments MAY use other URI schemes (e.g., HTTPS URLs or
  URN:UUID identifiers).

aud:
: REQUIRED.  StringOrURI or array of StringOrURI.  The intended
  recipient(s) of the ECT.  The "aud" claim SHOULD contain the
  identifiers of all entities that will verify the ECT.  When
  an ECT must be verified by both the next agent and the audit
  ledger independently, "aud" MUST be an array containing both
  identifiers.  Each verifier checks that its own identity
  appears in "aud".

iat:
: REQUIRED.  NumericDate.  The time at which the ECT was issued.

exp:
: REQUIRED.  NumericDate.  The expiration time of the ECT.
  Implementations SHOULD set this to 5 to 15 minutes after "iat".

jti:
: REQUIRED.  String.  A unique identifier for both the ECT and
  the task it records, in UUID format {{RFC9562}}.  The "jti"
  serves as both the token identifier (for replay detection) and
  the task identifier (for DAG parent references in "par").
  Receivers MUST reject ECTs whose "jti" has already been seen
  within the expiration window.  When "wid" is present,
  uniqueness is scoped to the workflow; when "wid" is absent,
  uniqueness MUST be enforced globally across the ECT store.

### Execution Context {#exec-claims}

The following claims are defined by this specification:

wid:
: OPTIONAL.  String.  A workflow identifier that groups related
  ECTs into a single workflow.  When present, MUST be a UUID
  {{RFC9562}}.

exec_act:
: REQUIRED.  String.  The action or task type identifier describing
  what the agent performed (e.g., "process_payment",
  "validate_safety").  This claim name avoids collision with the
  "act" (Actor) claim registered by {{RFC8693}}.

par:
: REQUIRED.  Array of strings.  Parent task identifiers
  representing DAG dependencies.  Each element MUST be the "jti"
  value of a previously verified ECT.  An empty array indicates
  a root task with no dependencies.  A workflow MAY contain
  multiple root tasks.

### Data Integrity {#data-integrity-claims}

The following claims provide integrity verification for task
inputs and outputs without revealing the data itself:

inp_hash:
: OPTIONAL.  String.  The base64url encoding (without padding) of
  the SHA-256 hash of the input data, computed over the raw octets
  of the input.  SHA-256 is the mandatory algorithm with no
  algorithm prefix in the value, consistent with {{RFC9449}} and
  {{I-D.ietf-wimse-s2s-protocol}}.

out_hash:
: OPTIONAL.  String.  The base64url encoding (without padding) of
  the SHA-256 hash of the output data, using the same format as
  "inp_hash".

### Extensions {#extension-claims}

ext:
: OPTIONAL.  Object.  A general-purpose extension object for
  domain-specific claims not defined by this specification.
  Implementations that do not understand extension claims MUST
  ignore them.  Extension key names SHOULD use reverse domain
  notation (e.g., "com.example.custom_field") to avoid
  collisions.  The serialized "ext" object SHOULD NOT exceed
  4096 bytes and SHOULD NOT exceed a nesting depth of 5 levels.

## Complete ECT Example

The following is a complete ECT payload example:

~~~json
{
  "iss": "spiffe://example.com/agent/clinical",
  "aud": "spiffe://example.com/agent/safety",
  "iat": 1772064150,
  "exp": 1772064750,
  "jti": "550e8400-e29b-41d4-a716-446655440001",

  "wid": "a0b1c2d3-e4f5-6789-abcd-ef0123456789",
  "exec_act": "recommend_treatment",
  "par": [],

  "inp_hash": "n4bQgYhMfWWaL-qgxVrQFaO_TxsrC4Is0V1sFbDwCgg",
  "out_hash": "LCa0a2j_xo_5m0U8HTBBNBNCLXBkg7-g-YpeiGJm564",

  "ext": {
    "com.example.trace_id": "abc123"
  }
}
~~~
{: #fig-full-ect title="Complete ECT Payload Example"}

# HTTP Header Transport {#http-header}

## Execution-Context Header Field

This specification defines the Execution-Context HTTP header field
{{RFC9110}} for transporting ECTs between agents.

The header field value is the ECT in JWS Compact Serialization
format {{RFC7515}}.  The value consists of three Base64url-encoded
parts separated by period (".") characters.

An agent sending a request to another agent includes the
Execution-Context header alongside the WIMSE Workload-Identity
header.  When a Workload Proof Token (WPT) is available per
{{I-D.ietf-wimse-s2s-protocol}}, agents SHOULD include it
alongside the WIT and ECT.

~~~
GET /api/safety-check HTTP/1.1
Host: safety-agent.example.com
Workload-Identity: eyJhbGci...WIT...
Execution-Context: eyJhbGci...ECT...
~~~
{: #fig-http-example title="HTTP Request with ECT Header"}

When multiple parent tasks contribute context to a single request,
multiple Execution-Context header field lines MAY be included, each
carrying a separate ECT in JWS Compact Serialization format.

When a receiver processes multiple Execution-Context headers, it
MUST individually verify each ECT per the procedure in
{{verification}}.  If any single ECT fails verification, the
receiver MUST reject the entire request.  The set of verified
parent task IDs across all received ECTs represents the complete
set of parent dependencies available for the receiving agent's
subsequent ECT.

# DAG Validation {#dag-validation}

ECTs form a Directed Acyclic Graph (DAG) where each task
references its parent tasks via the "par" claim.  DAG validation
is performed against the ECT store — either an audit ledger or
the set of parent ECTs received inline.

When receiving and verifying an ECT, implementations MUST perform
the following DAG validation steps:

1.  Task ID Uniqueness: The "jti" claim MUST be unique within the
    applicable scope (the workflow identified by "wid", or the
    entire ECT store if "wid" is absent).  If an ECT with the same
    "jti" already exists, the ECT MUST be rejected.

2.  Parent Existence: Every task identifier listed in the "par"
    array MUST correspond to a task that is available in the ECT
    store (either previously recorded in the ledger or received
    inline as a verified parent ECT).  If any parent task is not
    found, the ECT MUST be rejected.

3.  Temporal Ordering: The "iat" value of every parent task MUST
    NOT be greater than the "iat" value of the current task plus a
    configurable clock skew tolerance (RECOMMENDED: 30 seconds).
    That is, for each parent: `parent.iat < child.iat +
    clock_skew_tolerance`.  The tolerance accounts for clock skew
    between agents; it does not guarantee strict causal ordering
    from timestamps alone.  Causal ordering is primarily enforced
    by the DAG structure (parent existence in the ECT store), not by
    timestamps.  If any parent task violates this constraint, the
    ECT MUST be rejected.

4.  Acyclicity: Following the chain of parent references MUST NOT
    lead back to the current ECT's "jti".  If a cycle is detected,
    the ECT MUST be rejected.

5.  Trust Domain Consistency: Parent tasks SHOULD belong to the
    same trust domain or to a trust domain with which a federation
    relationship has been established.

To prevent denial-of-service via extremely deep or wide DAGs,
implementations SHOULD enforce a maximum ancestor traversal limit
(RECOMMENDED: 10000 nodes).  If the limit is reached before cycle
detection completes, the ECT SHOULD be rejected.

In distributed deployments, a parent ECT may not yet be available
locally due to replication lag.  Implementations MAY defer
validation to allow parent ECTs to arrive, but MUST NOT treat
the ECT as verified until all parent references are resolved.

# Signature and Token Verification {#verification}

## Verification Procedure

When an agent receives an ECT, it MUST perform the following
verification steps in order:

1.  Parse the JWS Compact Serialization to extract the JOSE header,
    payload, and signature components per {{RFC7515}}.

2.  Verify that the "typ" header parameter is "wimse-exec+jwt".

3.  Verify that the "alg" header parameter appears in the
    verifier's configured allowlist of accepted signing algorithms.
    The allowlist MUST NOT include "none" or any symmetric
    algorithm (e.g., HS256, HS384, HS512).  Implementations MUST
    include ES256 in the allowlist; additional asymmetric algorithms
    MAY be included per deployment policy.

4.  Verify the "kid" header parameter references a known, valid
    public key from a WIT within the trust domain.

5.  Retrieve the public key identified by "kid" and verify the JWS
    signature per {{RFC7515}} Section 5.2.

6.  Verify that the signing key identified by "kid" has not been
    revoked within the trust domain.  Implementations MUST check
    the key's revocation status using the trust domain's key
    lifecycle mechanism (e.g., certificate revocation list, OCSP,
    or SPIFFE trust bundle updates).

7.  Verify the "alg" header parameter matches the algorithm in the
    corresponding WIT.

8.  Verify the "iss" claim matches the "sub" claim of the WIT
    associated with the "kid" public key.

9.  Verify the "aud" claim contains the verifier's own workload
    identity.  When "aud" is an array, it is sufficient that the
    verifier's identity appears as one element; the presence of
    other audience values does not cause verification failure.
    When the verifier is the audit ledger, the ledger's own
    identity MUST appear in "aud".

10. Verify the "exp" claim indicates the ECT has not expired.

11. Verify the "iat" claim is not unreasonably far in the past
    (implementation-specific threshold, RECOMMENDED maximum of
    15 minutes) and is not unreasonably far in the future
    (RECOMMENDED: no more than 30 seconds ahead of the
    verifier's current time, to account for clock skew).

12. Verify all required claims ("jti", "exec_act", "par") are
    present and well-formed.

13. Perform DAG validation per {{dag-validation}}.

14. If all checks pass and an audit ledger is deployed, the ECT
    SHOULD be appended to the ledger.

If any verification step fails, the ECT MUST be rejected and the
failure MUST be logged for audit purposes.  Error messages
SHOULD NOT reveal whether specific parent task IDs exist in the
ECT store, to prevent information disclosure.

When ECT verification fails during HTTP request processing, the
receiving agent SHOULD respond with HTTP 403 (Forbidden) if the
WIT is valid but the ECT is invalid, and HTTP 401
(Unauthorized) if the ECT signature verification fails.  The
response body SHOULD include a generic error indicator without
revealing which specific verification step failed.  The receiving
agent MUST NOT process the requested action when ECT verification
fails.

# Audit Ledger Interface {#ledger-interface}

ECTs MAY be recorded in an immutable audit ledger for compliance
verification and post-hoc analysis.  A ledger is RECOMMENDED for
regulated environments but is not required for point-to-point
operation.  This specification does not mandate a specific storage
technology.  Implementations MAY use append-only logs, databases
with cryptographic commitment schemes, distributed ledgers, or
any storage mechanism that provides the required properties.

When an audit ledger is deployed, the implementation MUST provide:

1.  Append-only semantics: Once an ECT is recorded, it MUST NOT be
    modified or deleted.

2.  Ordering: The ledger MUST maintain a total ordering of ECT
    entries via a monotonically increasing sequence number.

3.  Lookup by ECT ID: The ledger MUST support efficient retrieval
    of ECT entries by "jti" value.

4.  Integrity verification: The ledger SHOULD provide a mechanism
    to verify that no entries have been tampered with (e.g.,
    hash chains or Merkle trees).

The ledger SHOULD be maintained by an entity independent of the
workflow agents to reduce the risk of collusion.

# Security Considerations

## Threat Model

The threat model considers: (1) a malicious agent that creates
false ECT claims, (2) an agent whose private key has been
compromised, (3) a ledger tamperer attempting to modify recorded
entries, and (4) a time manipulator altering timestamps to affect
perceived ordering.

## Self-Assertion Limitation {#self-assertion-limitation}

ECTs are self-asserted by the executing agent.  The agent claims
what it did, and this claim is signed with its private key.  A
compromised or malicious agent could create ECTs with false claims
(e.g., claiming an action was performed when it was not).

ECTs do not independently verify that:

- The claimed execution actually occurred as described
- The input/output hashes correspond to the actual data processed
- The agent faithfully performed the stated action

The trustworthiness of ECT claims depends on the trustworthiness
of the signing agent and the integrity of the broader deployment
environment.  ECTs provide a technical mechanism for execution
recording; they do not by themselves satisfy any specific
regulatory compliance requirement.

## Signature Verification

ECTs MUST be signed with the agent's private key using JWS
{{RFC7515}}.  The signature algorithm MUST match the algorithm
specified in the agent's WIT.  Receivers MUST verify the ECT
signature against the WIT public key before processing any
claims.  Receivers MUST verify that the signing key has not been
revoked within the trust domain (see step 6 in
{{verification}}).

If signature verification fails or if the signing key has been
revoked, the ECT MUST be rejected entirely and the failure MUST
be logged.

Implementations MUST use established JWS libraries and MUST NOT
implement custom signature verification.

## Replay Attack Prevention

ECTs include short expiration times (RECOMMENDED: 5-15 minutes)
and audience restriction via "aud" to limit replay attacks.
Implementations MUST maintain a cache of recently-seen "jti"
values and MUST reject ECTs with duplicate "jti" values.  Each
ECT is cryptographically bound to the issuing agent via "kid";
verifiers MUST confirm that "kid" resolves to the "iss" agent's
key (step 8 in {{verification}}).

## Man-in-the-Middle Protection

ECTs MUST be transmitted over TLS or mTLS connections.  When used
with {{I-D.ietf-wimse-s2s-protocol}}, transport security is
already established.

## Key Compromise

If an agent's private key is compromised, an attacker can forge
ECTs that appear to originate from that agent.  Mitigations:

- Implementations SHOULD use short-lived keys and rotate them
  frequently.
- Private keys SHOULD be stored in hardware security modules or
  equivalent secure key storage.
- Trust domains MUST support rapid key revocation.

ECTs recorded before key revocation remain valid historical
records but SHOULD be flagged for audit purposes.  New ECTs
MUST NOT reference a parent ECT whose signing key is known to
be revoked at creation time.

## Collusion and DAG Integrity {#collusion-and-false-claims}

A single malicious agent cannot forge parent task references
because DAG validation requires parent tasks to exist in the ECT
store.  However, multiple colluding agents could create a false
execution history.  Additionally, a malicious agent may omit
actual parent dependencies from "par" to hide influences on its
output; because ECTs are self-asserted
({{self-assertion-limitation}}), no mechanism can force complete
dependency declaration.

Mitigations include:

- The ledger SHOULD be maintained by an entity independent of the
  workflow agents.
- Multiple independent ledger replicas can be compared for
  consistency.
- External auditors can compare the declared DAG against expected
  workflow patterns.

Verifiers SHOULD validate that the declared "wid" of parent ECTs
matches the "wid" of the child ECT, rejecting cross-workflow
parent references unless explicitly permitted by deployment
policy.

## Privilege Escalation via ECTs

ECTs record execution history; they do not convey authorization.
Verifiers MUST NOT interpret the presence of an ECT, or a
particular set of parent references in "par", as an authorization
grant.  Authorization decisions MUST remain with the identity and
authorization layer (WIT, WPT, and deployment policy).

## Denial of Service

Implementations SHOULD apply rate limiting to prevent excessive
ECT submissions.  DAG validation SHOULD be performed after
signature verification to avoid wasting resources on unsigned
tokens.

## Timestamp Accuracy

Implementations SHOULD use synchronized time sources (e.g., NTP)
and SHOULD allow a configurable clock skew tolerance (RECOMMENDED:
30 seconds).  Cross-organizational deployments MAY require a
higher tolerance and SHOULD document the configured value.

## ECT Size Constraints

Implementations SHOULD limit the "par" array to a maximum of
256 entries.  See {{extension-claims}} for "ext" size limits.

# Privacy Considerations

## Data Exposure in ECTs

ECTs necessarily reveal:

- Agent identities ("iss", "aud") for accountability purposes
- Action descriptions ("exec_act") for audit trail completeness
- Timestamps ("iat", "exp") for temporal ordering

ECTs are designed to NOT reveal:

- Actual input or output data values (replaced with cryptographic
  hashes via "inp_hash" and "out_hash")
- Internal computation details or intermediate steps
- Proprietary algorithms or intellectual property
- Personally identifiable information (PII)

## Data Minimization {#data-minimization}

Implementations SHOULD minimize the information included in ECTs.
The "exec_act" claim SHOULD use structured identifiers (e.g.,
"process_payment") rather than natural language descriptions.
Extension keys in "ext" ({{extension-claims}}) deserve particular
attention: human-readable values risk exposing sensitive operational
details.  See {{extension-claims}} for guidance on using
structured identifiers.

## Storage and Access Control

ECTs stored in audit ledgers SHOULD be access-controlled so that
only authorized auditors can read them.  Implementations SHOULD
consider encryption at rest for ledger storage.  ECTs provide
structural records of execution ordering; they are not intended
for public disclosure.

Full input and output data (corresponding to the hashes in ECTs)
SHOULD be stored separately from the ledger with additional access
controls, since auditors may need to verify hash correctness but
general access to the data values is not needed.

# IANA Considerations

## Media Type Registration

This document requests registration of the following media type
in the "Media Types" registry maintained by IANA:

Type name:
: application

Subtype name:
: wimse-exec+jwt

Required parameters:
: none

Optional parameters:
: none

Encoding considerations:
: 8bit; an ECT is a JWT that is a JWS using the Compact
  Serialization, which is a sequence of Base64url-encoded values
  separated by period characters.

Security considerations:
: See the Security Considerations section of this document.

Interoperability considerations:
: none

Published specification:
: This document

Applications that use this media type:
: Applications that implement agentic workflows requiring execution
  context tracing and audit trails.

Additional information:
: Magic number(s): none
  File extension(s): none
  Macintosh file type code(s): none

Person and email address to contact for further information:
: Christian Nennemann, ietf@nennemann.de

Intended usage:
: COMMON

Restrictions on usage:
: none

Author:
: Christian Nennemann

Change controller:
: IETF

## HTTP Header Field Registration {#header-registration}

This document requests registration of the following header field
in the "Hypertext Transfer Protocol (HTTP) Field Name Registry"
maintained by IANA:

Field name:
: Execution-Context

Status:
: permanent

Specification document:
: This document, {{http-header}}

## JWT Claims Registration {#claims-registration}

This document requests registration of the following claims in
the "JSON Web Token Claims" registry maintained by IANA:

| Claim Name | Claim Description | Change Controller | Reference |
|:---:|:---|:---:|:---:|
| wid | Workflow Identifier | IETF | {{exec-claims}} |
| exec_act | Action/Task Type | IETF | {{exec-claims}} |
| par | Parent Task Identifiers | IETF | {{exec-claims}} |
| inp_hash | Input Data Hash | IETF | {{data-integrity-claims}} |
| out_hash | Output Data Hash | IETF | {{data-integrity-claims}} |
| ext | Extension Object | IETF | {{extension-claims}} |
{: #table-claims title="JWT Claims Registrations"}

--- back

# Use Cases {#use-cases}
{:numbered="false"}

This section describes a representative use case demonstrating how
ECTs provide structured execution records.

Note: task identifiers in this section are abbreviated for
readability.  In production, all "jti" values are required to be
UUIDs per {{exec-claims}}.

## Cross-Organization Financial Trading
{:numbered="false"}

In a cross-organization trading workflow, an investment bank's
agents coordinate with an external credit rating agency.  The
agents operate in separate trust domains with a federation
relationship.  The DAG records that independent assessments from
both organizations were completed before trade execution.

~~~
Trust Domain: bank.example
  Agent A1 (Portfolio Risk):
    jti: task-001    par: []
    iss: spiffe://bank.example/agent/risk
    exec_act: analyze_portfolio_risk

Trust Domain: ratings.example (external)
  Agent B1 (Credit Rating):
    jti: task-002    par: []
    iss: spiffe://ratings.example/agent/credit
    exec_act: assess_credit_rating

Trust Domain: bank.example
  Agent A2 (Compliance):
    jti: task-003    par: [task-001, task-002]
    iss: spiffe://bank.example/agent/compliance
    exec_act: verify_trade_compliance

  Agent A3 (Execution):
    jti: task-004    par: [task-003]
    iss: spiffe://bank.example/agent/execution
    exec_act: execute_trade
~~~
{: #fig-finance title="Cross-Organization Trading Workflow"}

The resulting DAG:

~~~
task-001 (analyze_portfolio_risk)   task-002 (assess_credit_rating)
  [bank.example]                      [ratings.example]
          \                              /
           v                            v
         task-003 (verify_trade_compliance)
           [bank.example]
                    |
                    v
         task-004 (execute_trade)
           [bank.example]
~~~
{: #fig-finance-dag title="Cross-Organization DAG"}

Task 003 has two parents from different trust domains,
demonstrating cross-organizational fan-in.  The compliance agent
verifies both parent ECTs — one signed by a local key and one by
a federated key from the rating agency's trust domain.

# Related Work
{:numbered="false"}

## WIMSE Workload Identity
{:numbered="false"}

The WIMSE architecture {{I-D.ietf-wimse-arch}} and service-to-
service protocol {{I-D.ietf-wimse-s2s-protocol}} provide the
identity foundation upon which ECTs are built.  WIT/WPT answer
"who is this agent?" and "does it control the claimed key?" while
ECTs record "what did this agent do?"  Together they form an
identity-plus-accountability framework for regulated agentic
systems.

## OAuth 2.0 Token Exchange and the "act" Claim
{:numbered="false"}

{{RFC8693}} defines the OAuth 2.0 Token Exchange protocol and
registers the "act" (Actor) claim in the JWT Claims registry.
The "act" claim creates nested JSON objects representing a
delegation chain: "who is acting on behalf of whom."  While
the nesting superficially resembles a chain, it is strictly
linear (each "act" object contains at most one nested "act"),
represents authorization delegation rather than task execution,
and carries no task identifiers or input/output integrity
data.  The "act" chain cannot represent
branching (fan-out) or convergence (fan-in) and therefore
cannot form a DAG.

ECTs intentionally use the distinct claim name "exec_act" for the
action/task type to avoid collision with the "act" claim.  The
two concepts are orthogonal: "act" records "who authorized whom,"
ECTs record "what was done, in what order."

## Transaction Tokens
{:numbered="false"}

OAuth Transaction Tokens {{I-D.ietf-oauth-transaction-tokens}}
propagate authorization context across workload call chains.
The Txn-Token "req_wl" claim accumulates a comma-separated list
of workloads that requested replacement tokens, which is the
closest existing mechanism to call-chain recording.

However, "req_wl" cannot form a DAG because:

- It is linear: a comma-separated string with no branching or
  merging representation.  When a workload fans out to multiple
  downstream services, each receives the same "req_wl" value and
  the branching is invisible.
- It is incomplete: only workloads that request a replacement
  token from the Transaction Token Service appear in "req_wl";
  workloads that forward the token unchanged are not recorded.
- It carries no task-level granularity, no parent references,
  and no execution content.
- It cannot represent convergence (fan-in): when two independent
  paths must both complete before a dependent task proceeds, a
  linear "req_wl" string cannot express that relationship.

Extensions for agentic use cases
({{I-D.oauth-transaction-tokens-for-agents}}) add agent
identity and constraints ("agentic_ctx") but no execution
ordering or DAG structure.

ECTs and Transaction Tokens are complementary: a Txn-Token
propagates authorization context ("this request is authorized
for scope X on behalf of user Y"), while an ECT records
execution accountability ("task T was performed, depending on
tasks P1 and P2").  An
agent request could carry both a Txn-Token for authorization
and an ECT for execution recording.  The WPT "tth" claim
defined in {{I-D.ietf-wimse-s2s-protocol}} can hash-bind a
WPT to a co-present Txn-Token; a similar binding mechanism
for ECTs is a potential future extension.

## Distributed Tracing (OpenTelemetry)
{:numbered="false"}

OpenTelemetry {{OPENTELEMETRY}} and similar distributed tracing
systems provide observability for debugging and monitoring.  ECTs
differ in several important ways: ECTs are cryptographically
signed per-task with the agent's private key; ECTs are
tamper-evident through JWS signatures; ECTs enforce DAG validation
rules; and ECTs are designed for regulatory audit rather than
operational monitoring.  OpenTelemetry data is typically controlled
by the platform operator and can be modified or deleted without
detection.  ECTs and distributed traces are complementary: traces
provide observability while ECTs provide signed execution records.
ECTs may reference OpenTelemetry trace identifiers in the "ext"
claim for correlation.

## W3C Provenance Data Model (PROV)
{:numbered="false"}

The W3C PROV Data Model defines an Entity-Activity-Agent ontology
for representing provenance information.  PROV's concepts map
closely to ECT structures: PROV Activities correspond to ECT
tasks, PROV Agents correspond to WIMSE workloads, and PROV's
"wasInformedBy" relation corresponds to ECT "par" references.
However, PROV uses RDF/OWL ontologies designed for post-hoc
documentation, while ECTs are runtime-embeddable JWT tokens with
cryptographic signatures.  ECT audit data could be exported to
PROV format for interoperability with provenance-aware systems.

## SCITT (Supply Chain Integrity, Transparency, and Trust)
{:numbered="false"}

The SCITT architecture {{I-D.ietf-scitt-architecture}} defines a
framework for transparent and auditable supply chain records.
ECTs and SCITT are complementary: the ECT "wid" claim can serve
as a correlation identifier in SCITT Signed Statements, linking
an ECT audit trail to a supply chain transparency record.

# Acknowledgments
{:numbered="false"}

The author thanks the WIMSE working group for their foundational
work on workload identity in multi-system environments.  The
concepts of Workload Identity Tokens and Workload Proof Tokens
provide the identity foundation upon which execution context
tracing is built.