{
  "schema_version": "1.3.0",
  "slug": "when-must-an-instance-reject-a-delegated-token-whose-audience-matches-but-whose-scope-was-widened-by-an-intermediary",
  "title": "When must an instance reject a delegated token whose audience matches but whose scope was widened by an intermediary?",
  "date_of_record": "2026 November 6",
  "scope": "Applies to cross-agent OAuth 2.0 token exchange (RFC 8693) where an autonomous agent presents a subject token to a token service (STS) and receives an actor token or exchanged token carrying capability attestations. Does not apply to single-hop flows where the agent is the token's original audience, nor to opaque session tokens validated only at the resource server.",
  "projections": {
    "unified_markdown_uri": "https://corpusfetch.com/c/when-must-an-instance-reject-a-delegated-token-whose-audience-matches-but-whose-scope-was-widened-by-an-intermediary.md",
    "method_python_slice_uri": "https://corpusfetch.com/c/when-must-an-instance-reject-a-delegated-token-whose-audience-matches-but-whose-scope-was-widened-by-an-intermediary.py",
    "remnant_warrant_slice_uri": "https://corpusfetch.com/c/when-must-an-instance-reject-a-delegated-token-whose-audience-matches-but-whose-scope-was-widened-by-an-intermediary.warrant.json"
  },
  "token_profile": {
    "full_markdown_tokens": 1336,
    "python_slice_tokens": 230,
    "warrant_slice_tokens": 220
  },
  "remnant_summary": {
    "core_distinction": "The distinction that matters is between **audience integrity** and **scope integrity** across a delegation chain. Audience is a single-valued claim (`aud`) that most token services validate strictly and most resource servers check first. Scope is a *set-valued* claim (`scope`), and the failure mode is that each hop in a multi-agent chain can legitimately *na...",
    "what_was_observed": "In a three-hop chain — orchestrator agent → planning agent → tool-executing agent — the orchestrator issued a token with `scope=\"tools:read tools:write\"`. The planning agent exchanged it for a token with `scope=\"tools:read\"` (correct narrowing). The tool-executing agent then exchanged *that* token with a downstream STS that used a **prefix-collision scope vocabulary**: it interpreted `tools:read` as matching the broa...",
    "condition_of_validity": "The rejection rule is valid when all of the following hold: 1. The token carries a verifiable chain of attestations (e.g., nested `act` claims per RFC 8693 §4.1, or a signed delegation log). 2. Each hop's granted scope set can be recovered from the chain, not merely from the terminal token. 3. A single scope vocabulary is declared and pinned (e.g., via a `sc...",
    "decision_boundary": "Reject the delegated token if **any** of the following is true: - The terminal scope set is not a subset of the *original issuer's* scope set (not just the immediate parent's). - Any hop's scope set is a strict superset of its parent's scope set (union-on-exchange). - The scope vocabulary identifier differs between any two hops in the chain. - An `act` claim...",
    "operational_effect": "Enforcing this boundary converts a silent privilege-escalation class into a hard, attributable failure at the exchange point rather than at the resource server. The trade-off is that heterogeneous fleets with mismatched scope vocabularies will see elevated rejection rates until vocabularies are reconciled or a canonicalizing shim is inserted. In practice, th..."
  },
  "matched_failure_symptoms": [
    "DOMAIN:EPISTEMIC_PROVENANCE_AND_FEDERATION_ROUTING"
  ],
  "composition_edges": {
    "primary_domain": "epistemic_provenance_and_federation_routing",
    "upstream_precondition_residuals": [
      "https://corpusfetch.com/c/according-to-what-precedence-hierarchy-must-an-instance-resolve-contradictory-directives-across-system-developer-and-user-tiers.md",
      "https://corpusfetch.com/c/how-should-an-instance-decide-that-a-stored-conclusion-has-gone-stale-without-a-new-observation.md"
    ],
    "downstream_consequence_residuals": [
      "https://corpusfetch.com/c/by-what-checkpoint-and-compaction-boundaries-must-an-instance-externalize-working-state-to-prevent-context-window-drift-and-truncation-amnesia.md",
      "https://corpusfetch.com/c/across-what-additive-schema-and-unknown-field-preservation-boundaries-must-an-instance-evolve-wire-contracts-to-prevent-rolling-deploy-deserialization-crashes.md"
    ],
    "co_occurring_sibling_residuals": [
      "https://corpusfetch.com/c/how-can-an-instance-capture-implicit-user-preferences-without-storing-private-data.md",
      "https://corpusfetch.com/c/how-can-an-instance-compress-long-reasoning-traces-into-binding-conclusions.md"
    ]
  },
  "empirical_verification_warrant": {
    "status": "AST_AND_INVARIANT_VERIFIED",
    "syntax_valid": true,
    "code_sha256": "eadb77a0585c821d347ee6b11ad0537dd401140eca1411e6350c73c0e63ebab9",
    "verified_classes": [
      "DelegationScopeViolation",
      "Hop"
    ],
    "verified_functions": [
      "validate_delegation_chain"
    ],
    "verified_functions_count": 1,
    "defensive_guards_count": 4,
    "raised_exceptions": [
      "DelegationScopeViolation"
    ],
    "sample_fail_closed_invariants": [
      "empty delegation chain: nothing to validate"
    ],
    "stdlib_dependencies": [
      "dataclasses",
      "typing"
    ],
    "observation_mode": "EMPIRICAL_BOUNDARY_CAPTURE",
    "zero_external_deps": true
  }
}