Mission-Bound Runtime Enforcement for OAuth 2.0

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Table of Contents

1. Introduction

Mission-Bound Authorization for OAuth 2.0 [I-D.draft-mcguinness-oauth-mission] (the "issuance profile") makes a Mission a first-class OAuth artifact: a structured, human-approved, integrity-bound task whose authority bounds and outlives every token an agent derives. But it is deliberately an issuance-and-derivation layer. As its security considerations state, it does not evaluate individual runtime actions, so an active Mission still bounds a set of authority an agent may exercise freely within a token's lifetime, and preventing that authority from becoming ambient for individual consequential actions requires a separate runtime enforcement layer.¶

This document is that layer. It delivers exactly the four things the issuance profile names as out of scope, plus enforcement of the constraints that profile carries but does not evaluate:¶

1. evaluation of a request's parameters against the Mission at the point of use (Section 6, Section 7);¶

2. per-action runtime enforcement evidence (Section 10);¶

3. binding of the invoked tool or function identity to the Mission's approved authority (Section 6);¶

4. execution-time re-evaluation that closes the approval-to-execution (time-of-check to time-of-use) gap (Section 7);¶

and, additionally, metering of the consumption bounds (budget, call counts, duration) the issuance profile carries as constraints but leaves to this layer to enforce (Section 8).¶

The model is a Policy Enforcement Point (PEP) at each consequential execution boundary that, before the action runs, obtains a decision from a Policy Decision Point (PDP) evaluating the action against the Mission. Issuance is governance; this is enforcement.¶

2. Overview

 Agent          PEP (action boundary)        PDP
   |                  |                        |
   |- action+params ->|                        |
   |                  | validate token         |
   |                  |- evaluate vs Mission ->|
   |                  |  (authority, params,   |
   |                  |   actor, state)        |
   |                  |<---- permit / deny ----|
   |                  | bind to params;        |
   |                  | write evidence         |
   |<- execute/refuse-|                        |

3. Action classification

The boundary between consequential and non-consequential actions is deployment policy, but a deployment MUST NOT define it so loosely that nothing is enforced. This document defines a default classification a deployment SHOULD adopt, and a floor it MUST observe.¶

Classification floor. Actions in the irreversible, external commitment, and privileged administration classes MUST be treated as consequential and gated. A Mission's purpose, or deployment policy, MAY raise an action to a stricter class; it MUST NOT lower an action below the resource owner's minimum classification, and MUST NOT classify an irreversible, external-commitment, or privileged-administration action as non-consequential. A deployment that leaves such an action ungated does not enforce this profile for that action's class (Section 4).¶

A deployment policy can require human confirmation, step-up authentication, or another local signal for privileged administration or external commitments. This profile does not define such a signal.¶

4. PEP placement

Enforcement only works at the component that can actually stop the action. A deployment claiming this profile MUST observe these rules:¶

• The PEP MUST sit at the last controllable boundary before the action. A permit checked further upstream does not survive parameter changes, retries, or routing that happen after the check.¶

• A token-issuance decision does not replace execution-time authorization. A token-only Resource Server cannot claim runtime enforcement; the issuance gate is governance, the runtime gate is enforcement.¶

• A tool-catalog filter does not replace per-call authorization. Filtering a tool list by the caller's authority is exposure control; every consequential tool call MUST still pass the runtime gate.¶

• An orchestrator's internal check does not replace a Resource Server's PEP. Defense in depth is permitted; substitution is not.¶

• If no PEP can prevent the action for a given class, the deployment MUST NOT claim runtime enforcement for that class, and MUST name the action classes and execution paths it does mediate.¶

The boundary varies by action: an OAuth-protected API call is gated at the Resource Server; a consequential MCP tools/call at the MCP server; a local tool invocation, file write, or payment at the orchestrator or whatever component drives the call; external egress at an egress proxy. Where an action can be reached by an unmediated path (a debug shell, an unsanctioned egress route, a direct connector), the profile is not enforced for the classes that path reaches.¶

5. Token presentation and validation

The runtime decision is downstream of ordinary access token validation. Before using a token's Mission, authority, subject, client, actor, or confirmation-key values as decision inputs, the PEP MUST establish that the access token is valid for the protected resource and request. For the Mission-bound JWT access tokens defined by the issuance profile, this means validating the JWT per [RFC9068], verifying the issuer and audience, checking token expiry, and verifying any sender-constraint binding (cnf) according to the proof-of-possession profile in use.¶

A PEP MUST NOT ask a PDP to authorize an action from unverified token claims. If token validation fails, or if the deployment requires Mission governance for the protected operation and the token lacks a mission claim, the PEP MUST refuse before runtime Mission evaluation. When the PEP is an OAuth Resource Server, it uses the normal OAuth error behavior for the protected resource (for example, Bearer token errors under [RFC6750]); this profile defines no new OAuth error code.¶

Where the PEP and PDP are separate components, the decision request and response MUST be integrity-protected and the parties MUST authenticate each other. The PDP MUST accept token-derived inputs only from a PEP authorized for the declared enforcement scope. A deployment can satisfy this with a mutually authenticated channel, a signed decision request and response, or another mechanism with equivalent security properties.¶

6. The decision

Before a consequential action runs, its PEP MUST obtain a permit from a PDP that evaluates the action against the Mission the acting token is bound to. This is the normative contract. The decision API wire format is a deployment choice; Section 11 gives a non-normative example binding.¶

The PEP MUST supply, and the PDP MUST evaluate:¶

• Authority. The action MUST be authorized by an applicable authorization_details entry in the token. For an entry of type mission_resource_access, the action's resource and invoked action or tool identity MUST be within that entry's resource and actions, under the subset rule of [I-D.draft-mcguinness-oauth-mission]. The PEP asserts the capability identity (for example, the tool or function name) it will invoke; the PDP MUST refuse an identity outside the approved actions. For any other authorization_details type, the PDP MUST evaluate the action under that type's documented runtime semantics and MUST refuse if it does not understand or cannot enforce those semantics. Richer capability-source binding (source digests, cross-format identity) is out of scope (Section 12).¶

• Resource policy. The PDP MUST evaluate any applicable Resource policy. A Mission-bound token and runtime permit are an upper bound on authority, not a command for the Resource Server to perform the action. The PDP MUST refuse when Resource policy, object-level authorization, tenant configuration, legal holds, service invariants, or risk policy prohibit the action, even if the action is otherwise within the Mission authority.¶

• Parameters. Every machine-enforceable constraints value on the applicable entry MUST be evaluated against the concrete action parameters. A constraint the PDP does not understand or cannot meter MUST cause refusal; it MUST NOT be ignored.¶

• Actor. When delegation is in effect, the PDP MUST evaluate the authenticated act chain and refuse a chain that is missing, malformed, or references an actor not permitted for the entry. When an act chain is present, the PDP MUST NOT treat client_id alone as the immediate actor.¶

• Time. The PDP MUST refuse if the decision context indicates the token is expired or the requested action would execute outside the permit validity window. If its Mission state source reports that the Mission has expired, or reports a mission_expiry value that has passed, the PDP MUST refuse independent of the token's own exp.¶

• State. The PDP MUST refuse unless the Mission is active (Section 6.1).¶

On a deny, the PEP MUST refuse the action. Authority-expandable denials and the escalation workflow that turns a deny into a Mission expansion are out of scope and deferred (Section 12); in this profile a deny is terminal for the attempted action.¶

The PDP's placement is a deployment choice (co-located with the Mission's origin, embedded in the Resource Server, a tenant-scoped service, or a shared service); this document does not mandate one. The requirement is only that a PEP at each consequential boundary can reach an applicable PDP.¶

7. Parameter binding and time-of-check to time-of-use

A permit for an operation does not authorize arbitrary parameter values. For consequential writes, irreversible actions, external commitments, and privileged administration, the PDP MUST bind its permit to the normalized action parameters through a parameter_digest, and the executing PEP MUST recompute and reverify that digest immediately before acting.¶

• parameter_digest is sha-256: followed by the base64url, no padding, SHA-256 [RFC6234] of the JCS [RFC8785] serialization of the normalized parameter object. It MUST be computed under the same canonicalization rules the issuance profile defines (duplicate member rejection, significant array order, byte-for-byte URI comparison); this document does not define a second canonicalization.¶

• The operation profile MUST define default insertion, omitted optional fields, and set-like array handling before canonicalization.¶

• The permit MUST also bind the Mission reference, token issuer when available, token audience or protected resource, sub, client_id, actor context, sender-constraint confirmation key when present, action, resource, the authorizing authorization_details entry or an entry digest, the PDP's policy-view version, and either a short validity window or a single-use decision identifier.¶

• The executing PEP MUST verify those bindings and MUST recompute the parameter_digest against the parameters it is about to use. A mismatch MUST cause refusal: the permit does not authorize the changed parameters.¶

This closes the time-of-check to time-of-use gap and prevents a permit from being replayed for a different request. Consequential reads do not require a parameter digest; the evaluation request still appears in the evidence record, by digest where the parameters are sensitive (Section 10).¶

8. Consumption metering

Consumption bounds the Mission carries as constraints, such as a call count, a spend budget, or a duration, are enforced here, not at issuance. When an applicable entry (or the Mission's context) carries such a bound, the PDP MUST meter use against it and MUST refuse a consequential action that would exceed it.¶

The exactness of a consumption bound depends on the decision topology, and this profile does not overpromise:¶

• Under a single serializing PDP for the Mission, the check and decrement can be atomic, and the bound is exact.¶

• Under multiple or distributed PDPs (for example, Resource Server-hosted PDPs), an exact global counter is a distributed-counting problem. Such a deployment MUST publish the consistency bound it operates under (for example, per-PDP sub-budgets, or a bounded reconciliation window), and the effective guarantee is that bound, not exact-to-the-call enforcement.¶

A deployment MUST NOT advertise exact consumption enforcement it cannot meet under its chosen topology. As with all constraints, an unmetered or unrecognized consumption bound MUST cause refusal rather than silent pass-through.¶

For a metered permit, the PDP and PEP MUST define retry and idempotency behavior. A retry of the same normalized action under the same idempotency key or single-use decision identifier MUST NOT consume the bound twice. Reuse of an idempotency key or decision identifier for a different normalized action MUST cause refusal. For irreversible actions and external commitments, a deployment MUST define whether metering is reserved before execution and committed after success, or committed before execution; it MUST NOT leave the decrement ambiguous.¶

9. Failure modes

Enforcement is meaningful only if failure is bounded. A PDP or PEP MUST behave as follows; in all cases the evidence record (Section 10) MUST be sufficient to reconstruct which path produced a refusal.¶

10. Runtime enforcement evidence

Every PDP decision on a consequential action MUST produce a decision evidence record. A PEP refusal for a consequential action that occurs before a PDP decision (for example, token validation failure or PDP unreachability) or after a PDP permit (for example, parameter_digest mismatch) MUST also produce an enforcement evidence record with the available fields and the failure condition. This document fixes the record's content, its canonical form, and its local integrity; portable cross-domain receipts are out of scope (Section 12).¶

A record MUST contain:¶

• the decision or refusal result and, on refusal, the failure condition from Section 9;¶

• the request time (RFC 3339 [RFC3339]); and¶

• the parameter_digest for parameter-bound classes, or a privacy-preserving digest of the evaluation request otherwise.¶

A record MUST also contain the following fields when they are available and trusted for the refusal or decision path:¶

• the Mission reference (mission.id, mission.origin) and the authority_hash (and proposal_hash when known) it operated under;¶

• the token issuer and audience or protected-resource identifier when available;¶

• the authenticated sub, client_id, client-instance identifier when present, sender-constraint confirmation key when present, and the act chain projection when delegation applies;¶

• the action and resource identifiers (and the asserted capability identity when applicable);¶

• the authorization_details type and authorizing entry, or a digest of that entry when recording the full entry would disclose excess authority or sensitive policy;¶

• the decision identifier, when the PDP produced one; and¶

• the PDP's policy-view version.¶

For a token-validation failure, the record MUST NOT describe unverified token claims as authenticated facts. It MAY include a digest of the presented token or rejected claim set for correlation and forensics, subject to the privacy requirements below.¶

The authority_hash and proposal_hash in a record are the originating AS's commitments, cited as anchors; the PDP does not recompute them and is not required to hold the full Authority Set to record them, consistent with [I-D.draft-mcguinness-oauth-mission].¶

Requirements on the record:¶

• It MUST be serialized with JCS [RFC8785] before storage and integrity protection, under the issuance profile's canonicalization rules, so identical inputs from one PDP produce identical bytes.¶

• It MUST be append-only and integrity-protected; the deployment profile MUST name the mechanism (a hash-linked log, signed segments, a transparency anchor, or equivalent).¶

• Raw parameters MUST NOT appear in the record; when retained for forensics they MUST be in separately access-controlled storage referenced by an opaque identifier, with only the parameter_digest in the record.¶

• Records for one Mission MUST carry a deployment-defined sequence indicator so decision order can be reconstructed without relying on wall-clock time alone.¶

• The deployment profile MUST publish a retention window no shorter than the Mission's effective audit horizon.¶

11. Example decision API binding: AuthZEN

The decision contract of Section 6 is abstract. One possible binding is the OpenID AuthZEN Authorization API [AUTHZEN]: the PEP issues an Access Evaluation request and the PDP returns a decision. This section is non-normative and does not define an AuthZEN profile.¶

A deployment using AuthZEN can carry Mission and actor inputs in AuthZEN's open-ended context object:¶

• context.mission: id, origin, authority_hash, and the current state.¶

• context.actor: client_id, client-instance identifier when present, and the act chain as an array ordered root to leaf.¶

The AuthZEN subject remains the principal the decision is requested for. On permit, the response carries the policy-view version, a decision identifier, the parameter_digest for parameter-bound classes, and a short validity window.¶

This profile's substance is the enforcement contract, action classification (Section 3), PEP placement (Section 4), parameter binding (Section 7), consumption metering (Section 8), and runtime enforcement evidence (Section 10), which is independent of the decision wire. The context.mission and context.actor example members above could be standardized separately as a Mission-bound AuthZEN binding without changing this contract.¶

12. Out of scope

The following compose with this profile but are deferred to future work and are not required to enforce it:¶

• mission expansion and the authority-expandable-denial escalation workflow (a deny here is terminal for the attempted action);¶

• a standardized enforcement-scope manifest format and discovery mechanism;¶

• cross-format capability-source binding (signed capability manifests, source-digest drift handling, cross-catalog identity);¶

• portable, third-party-verifiable decision receipts (this profile fixes only the local runtime enforcement evidence record);¶

• separate Decision Evidence and Execution Evidence object schemas and media types;¶

• actor provenance beyond the act chain, attestation of the execution environment, and a purpose registry;¶

• compilation of the Mission into an engine-native policy artifact (Cedar, OpenFGA, or equivalent) and standardization of PDP deployment modes;¶

• action-hierarchy and resource-containment subset extensions (this profile uses the flat subset rule of [I-D.draft-mcguinness-oauth-mission]); and¶

• risk-signal inputs to the decision (deployment-defined).¶

Structured per-argument attenuation of tool grants ([I-D.draft-niyikiza-oauth-attenuating-agent-tokens]) is a related issuance/delegation-layer primitive, not part of this runtime profile.¶

13. Security Considerations

14. IANA Considerations

This document has no IANA actions. The non-normative context.mission and context.actor example members of Section 11 are not registered in an IETF registry. The Mission-bound token claims this profile consumes are registered by [I-D.draft-mcguinness-oauth-mission].¶

15. References

Acknowledgments

This document is the runtime companion to Mission-Bound Authorization for OAuth 2.0 and builds on the OpenID AuthZEN Authorization API and the OAuth 2.0 Rich Authorization Requests and JWT access token specifications.¶

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