Weave identity into the core concepts and repair the workstream links

docs/identity/overview.md

@@ -5,7 +5,7 @@
 
 There are 5 unique identity challenges that this standard aims to solve, where existing use cases that traditional identity models cannot support. It does not propose a wire format or normative requirements yet. Those will follow once the working group has aligned. This is an evolving space and we are taking a conservative approach with normative requirements.
 
-For taxonomy and definitions, see [Core Concepts](https://github.com/Agent-Control-Standard/ACS/blob/main/docs/topics/core_concepts.md).
+For taxonomy and definitions, see [Core Concepts](../topics/core_concepts.md), which introduces identity alongside the pillars and links back here.
 
 ## What's Changing with Agents
 
@@ -121,7 +121,7 @@ A concrete example that illustrates several of these challenges is Palo Alto Net
 | 1 | **Chain Integrity**<br/>*Can the full delegation chain be named and verified end-to-end?* | A single agent task can chain through five to ten identities: user → orchestrator → sub-agent → tool → downstream API. Two failures compound: the chain is not *named* (audit collapses into "the agent did it"), and the chain is not *verifiable* (downstream resources cannot confirm the chain without trusting every intermediary). In practice the full chain is often not reconstructable end-to-end, and there is a known class of attacks where the chain itself can be spliced. | **[OAuth 2.0](https://www.rfc-editor.org/rfc/rfc6749) access tokens** identify the bearer, not the chain.<br/>**[OIDC Core 1.0](https://openid.net/specs/openid-connect-core-1_0.html) ID tokens** name the human at the start but lose granularity at each hop.<br/>**[SPIFFE SVIDs](https://spiffe.io/docs/latest/spiffe-about/spiffe-concepts/)** identify the workload but not which call within it.<br/>**[OAuth Token Exchange (RFC 8693)](https://www.rfc-editor.org/rfc/rfc8693)** defines nested `act` claims that can express a chain, but per [§4.1](https://www.rfc-editor.org/rfc/rfc8693#section-4.1) *"prior actors identified by any nested `act` claims are informational only and are not to be considered in access control decisions."* The chain is recorded, not normatively enforceable.<br/>**[OAuth Identity Chaining draft](https://datatracker.ietf.org/doc/draft-ietf-oauth-identity-chaining/)** and **[Transaction Tokens draft](https://datatracker.ietf.org/doc/draft-ietf-oauth-transaction-tokens/)** address parts but specify neither chain verification rules nor revocation propagation as required runtime behavior.<br/>**[W3C Trace Context](https://www.w3.org/TR/trace-context/)** correlates but [does not authenticate](https://www.w3.org/TR/trace-context/#privacy-of-traceparent-field). | Every action must produce, at the moment of execution, a signed record that names the specific link in the chain and lets any participant (including the downstream resource) verify the entire chain end-to-end without trusting any intermediary. Cryptographic chain structure, mandatory scope attenuation at every hop, revocation propagation. | Pending |
 | 2 | **Over-Privilege**<br/>*Was this action within the agent's purpose?* | Agents inherit broad standing privileges. Service accounts. Long-lived API keys. OAuth scopes designed for human applications. One compromised agent has the union of every permission anyone has ever granted to it. The fix is not bigger scopes; the fix is no standing privilege. | **[OAuth scopes (RFC 6749 §3.3)](https://www.rfc-editor.org/rfc/rfc6749#section-3.3)** are coarse, deployment-defined strings (e.g. `read`, `write`, `repo`). Per **[RFC 9396 §1](https://www.rfc-editor.org/rfc/rfc9396#section-1)**, scope is "sufficient... for coarse-grained authorization requests" but "not sufficient to specify fine-grained authorization requirements" — it does not express per-action, per-resource, per-data-cell intent.<br/>**RBAC and ABAC** scope by role or attribute, granted once, evaluated coarsely.<br/>**AIMS** does not require **[RAR (RFC 9396)](https://www.rfc-editor.org/rfc/rfc9396)** and treats scope semantics as deployment-specific. | Credentials minted just before the call, scoped to one downstream callee, structured (per-action, per-resource), expired in minutes. Authorization evaluated per-call against the immutable intent for the run, not per-session. | Pending |
 | 3 | **Token Theft Resistance**<br/>*If a token leaks from agent memory, is it useless to the attacker?* | The agent threat model breaks OAuth's bearer-token assumption entirely. Prompt injection can exfiltrate tokens from memory. Tool outputs can leak tokens. Sub-agents can replay tokens. Logs and crash dumps capture tokens. Long-lived refresh tokens in agent memory are the worst case: a durable credential held in storage that any indirect prompt injection can read. | **[OAuth 2.0 Bearer Tokens (RFC 6750 §1.2)](https://www.rfc-editor.org/rfc/rfc6750#section-1.2)** explicitly treat possession as sufficient: *"Using a bearer token does not require a bearer to prove possession of cryptographic key material."*<br/>**API keys** are bearer secrets by definition.<br/>**[OAuth refresh tokens (RFC 6749 §1.5)](https://www.rfc-editor.org/rfc/rfc6749#section-1.5)** were designed for the same user returning later to resume a session, which does not describe how agents work.<br/>**[DPoP (RFC 9449)](https://www.rfc-editor.org/rfc/rfc9449)** and **[OAuth 2.0 Mutual-TLS Certificate-Bound Access Tokens (RFC 8705)](https://www.rfc-editor.org/rfc/rfc8705)** solve sender-constraint but are optional extensions that most deployments do not enforce.<br/>None of these are required by the OAuth core. | All non-trivial tokens sender-constrained (DPoP or mTLS) so a leaked token is useless without the corresponding private key. Aggressive lifetime ceilings measured in minutes or seconds, not hours. No long-lived secrets in model-visible context. Credentials fetched at task start, used within a tight window, discarded at task end. | Pending |
-| 4 | **Last-Mile Enforcement**<br/>*Did the resource actually enforce the decision, on every call, inside the runtime?* | The moment the action reaches a production system. All upstream identity work either holds here or fails here. Most systems today cannot distinguish an authorized action by an agent acting in good faith from the same call by an agent hijacked by indirect prompt injection. Gateway-only enforcement misses tool calls and sub-agent invocations that never cross a gateway. Cached decisions miss revocation, scope change, and freshly-discovered taint. | **API gateways and service meshes** enforce at the edge; agent tool calls never reach them.<br/>**[OAuth 2.0 resource servers (RFC 6749 §1.1)](https://www.rfc-editor.org/rfc/rfc6749#section-1.1)** validate the token but not the action's relationship to intent.<br/>**[mTLS (RFC 8705)](https://www.rfc-editor.org/rfc/rfc8705)** and **[SPIFFE](https://spiffe.io/docs/latest/spiffe-about/spiffe-concepts/)** establish workload identity but do not enforce per-action policy.<br/>None fire inside the agent runtime where the decision is made. | Enforcement fires at every tool call, inside the agent runtime, before the action executes. The runtime verifies identity, scope, taint, freshness, and intent on every call. The LLM call cost dwarfs the re-authorization cost, so caching decisions is not required for performance. Default-deny verified by a negative test in CI. | **Partially specified.** The ACS Instrument spec already defines the honoring-decisions contract in [§6.4 (Honoring Decisions, Normative)](https://github.com/Agent-Control-Standard/ACS/blob/main/docs/spec/instrument/specification.md#64-honoring-decisions-normative): the Observed Agent MUST wait for the Guardian's decision up to the negotiated timeout, MUST apply it, and MUST record every fail-open proceed as an audit event. Note the spec's current default on timeout is **fail-open with audit**, which is in tension with this row's default-deny / no-cache goal; whether identity-tier actions should tighten that to fail-closed is an open work item for this workstream. |
+| 4 | **Last-Mile Enforcement**<br/>*Did the resource actually enforce the decision, on every call, inside the runtime?* | The moment the action reaches a production system. All upstream identity work either holds here or fails here. Most systems today cannot distinguish an authorized action by an agent acting in good faith from the same call by an agent hijacked by indirect prompt injection. Gateway-only enforcement misses tool calls and sub-agent invocations that never cross a gateway. Cached decisions miss revocation, scope change, and freshly-discovered taint. | **API gateways and service meshes** enforce at the edge; agent tool calls never reach them.<br/>**[OAuth 2.0 resource servers (RFC 6749 §1.1)](https://www.rfc-editor.org/rfc/rfc6749#section-1.1)** validate the token but not the action's relationship to intent.<br/>**[mTLS (RFC 8705)](https://www.rfc-editor.org/rfc/rfc8705)** and **[SPIFFE](https://spiffe.io/docs/latest/spiffe-about/spiffe-concepts/)** establish workload identity but do not enforce per-action policy.<br/>None fire inside the agent runtime where the decision is made. | Enforcement fires at every tool call, inside the agent runtime, before the action executes. The runtime verifies identity, scope, taint, freshness, and intent on every call. The LLM call cost dwarfs the re-authorization cost, so caching decisions is not required for performance. Default-deny verified by a negative test in CI. | **Partially specified.** The ACS Instrument spec already defines the honoring-decisions contract in [§6.4 (Honoring Decisions, Normative)](../spec/instrument/specification.md#64-honoring-decisions-normative): the Observed Agent MUST wait for the Guardian's decision up to the negotiated timeout, MUST apply it, and MUST record every fail-open proceed as an audit event. Note the spec's current default on timeout is **fail-open with audit**, which is in tension with this row's default-deny / no-cache goal; whether identity-tier actions should tighten that to fail-closed is an open work item for this workstream. |
 | 5 | **Proof of Intent**<br/>*Was the action bound to an immutable, declared purpose that survives mid-task reframing?* | OAuth scopes say what the user *can* do. They do not say what the user *is doing right now*. Without intent binding at runtime, every agent action is a guess about user authorization. The agent's reasoning can be reframed mid-task by an instruction hidden in a document or a tool output. The original intent has to survive that. This is the hardest of the five, because it is the only one OAuth cannot patch with an extension: the underlying problem is non-deterministic client behavior under adversarial inputs. | **None at the identity layer.** Intent is implicit in the OAuth consent screen and discarded after token issuance.<br/>**[RFC 9396 RAR](https://www.rfc-editor.org/rfc/rfc9396)** can carry purpose claims as `authorization_details` data but does not bind them as runtime invariants against the LLM client.<br/>**IBAC (Intent-Based Access Control)** is research-stage with no IETF/W3C standard track.<br/>No production standard treats intent as a first-class, immutable, normatively-enforced runtime invariant. | Intent treated as a first-class governance concept with a normative immutability invariant. Intent must flow across all three ACS pillars: Instrument fires decisions against it, Trace records it as a span attribute, Inspect catalogs what it authorized. Intent extension permitted only through an explicit, human-approved path. | Pending |
 
 ---

docs/identity/standards.md

@@ -192,7 +192,7 @@ The following drafts are actively shaping identity for autonomous systems, AI ag
 
 ### Workload Identity (WIMSE)
 
-The WIMSE working group's workload identity stack that AIMS composes onto. This page **proposes** WIMSE identifiers as the recommended agent identifier, with SPIFFE SVIDs as a conformant implementation. Whether ACS mandates a specific identifier scheme is an open working group question. The normative position remains [docs/concepts/identity.md](https://github.com/Agent-Control-Standard/ACS/blob/main/docs/concepts/identity.md), which mandates no authentication mechanism and keeps identifier schemes off the wire; a deployment using `posix_uid` or `oauth_subject` stays conformant today.
+The WIMSE working group's workload identity stack that AIMS composes onto. This page **proposes** WIMSE identifiers as the recommended agent identifier, with SPIFFE SVIDs as a conformant implementation. Whether ACS mandates a specific identifier scheme is an open working group question. The normative position remains [docs/concepts/identity.md](../concepts/identity.md), which mandates no authentication mechanism and keeps identifier schemes off the wire; a deployment using `posix_uid` or `oauth_subject` stays conformant today.
 
 | Draft | Description | Link |
 |---|---|---|
@@ -268,7 +268,7 @@ If ACS and AIMS are positioned correctly, they are **complementary, not competin
 
 | Topic | Resolution |
 |---|---|
-| **Identifier model** | **Proposed: WIMSE identifier recommended, SPIFFE conformant.** Would align ACS with AIMS, WIMSE WG, and NIST. Pending WG sign-off and reconciliation with [docs/concepts/identity.md](https://github.com/Agent-Control-Standard/ACS/blob/main/docs/concepts/identity.md), which currently mandates no identifier scheme. |
+| **Identifier model** | **Proposed: WIMSE identifier recommended, SPIFFE conformant.** Would align ACS with AIMS, WIMSE WG, and NIST. Pending WG sign-off and reconciliation with [docs/concepts/identity.md](../concepts/identity.md), which currently mandates no identifier scheme. |
 | **Token lifetimes** | AIMS sets the baseline; proposed ACS ceilings (15 min LLM / 5 min MCP / 60 s high-risk) are open work items pending a normative spec clause. |
 | **Sender-constrained tokens** | Both require DPoP or mTLS. Cross-reference, no divergence. |
 | **Audit logging** | ACS identity blocks **extend** AIMS minimum audit event fields rather than diverging from them. |

docs/topics/core_concepts.md

@@ -19,6 +19,16 @@ A v0.1.0-conformant deployment implements **ACS-Core** (the Instrument baseline)
     - **Deterministic layer** (OPA/Rego, Cedar): always runs first.
     - **Agent layer** (LLM): invoked only when the deterministic layer's chain config delegates. Optional in v0.1; deterministic-only deployments are fully conformant.
 
+## Identity
+
+Identity answers who is acting. A **principal** is the authenticated party initiating or acting within a session. ACS keeps three identities distinct: which agent is under governance, which Guardian decided, and who authored the policy that produced the decision. Conflating them collapses an audit trail into "the agent did it."
+
+ACS invents no identity format. Descriptors carry a `type` discriminator naming the scheme (`posix_uid`, `oauth_subject`, `cert_subject`), and ACS stays agnostic to the rest. No authentication mechanism is mandated. Deployments declare the one they use at handshake, which binds ACS to the identity infrastructure an organization already runs.
+
+Identity is an upstream dependency of authorization: a capability decision is only as meaningful as the identity bound to it. An asserted identity is weaker than one bound by a verified credential, so policy gating high-impact actions should require the stronger rung. See [Concepts › Identity](../concepts/identity.md) and [Concepts › Trust basis](../concepts/trust.md).
+
+Runtime identity for agents raises problems that human and workload identity models do not answer, from delegation chains spanning five to ten hops to intent that must survive mid-task reframing. The Identity workstream tracks those as open work. See [Identity › Overview](../identity/overview.md) for the five runtime challenges and [Identity › Standards](../identity/standards.md) for where existing standards stop short.
+
 ## Vocabulary
 
 ACS scopes what it observes to a **session**, and within it to **turns** and **steps**. Each step produces a `ContextEntry` in the session's append-only audit chain, and the Guardian's verdict on it is one of five **dispositions** (`allow`, `deny`, `modify`, `ask`, `defer`).
@@ -60,6 +70,7 @@ ACS carries MCP and A2A intact. Wrapped MCP messages flow through `protocols/MCP
 ## Read Next
 
 - [Concepts](../concepts/README.md)
+- [Identity for Agents](../identity/overview.md)
 - [ACS in Action](./ACS_in_action_example.md)
 - [Conformance Profiles](../spec/conformance.md)
 - [Specification](../spec/instrument/specification.md)

mkdocs.yml

@@ -59,16 +59,16 @@ nav:
   - Concepts:
     - Overview: concepts/README.md
     - Agents: concepts/agents.md
-    - Identity: concepts/identity.md
+    - Identity:
+      - Overview: concepts/identity.md
+      - Identity for Agents: identity/overview.md
+      - Standards: identity/standards.md
     - Session Lifecycle: concepts/session-lifecycle.md
     - Intent: concepts/intent.md
     - Capability: concepts/capability.md
     - Skill: concepts/skill.md
     - Provenance: concepts/provenance.md
     - Trust Basis: concepts/trust.md
-  - Identity:
-    - Overview: identity/overview.md
-    - Standards: identity/standards.md
   - Specification:
     - Conformance Profiles: spec/conformance.md
     - Instrument: