HIPAA agent permission and delegated access architecture for enterprise LLM deployment — Reference Architecture

Reference architecture · published 2026-10-16 · regulated enterprise · HIPAA · layout spec_first · implementation executed in CI before publish

Technical parameters

Every value below is a parameter you can hold a vendor or an internal team to. Adjectives are not acceptance criteria.

The control that resolves this is an Intersecting Delegated Authority, evaluated before the request reaches a model provider rather than audited afterwards. In regulated enterprise the binding constraint is HIPAA, and the question it actually asks is can PHI reach a place the BAA does not cover. The shape below holds p95 ≤ 600ms over REST over HTTPS, and ships with a standard-library implementation that runs as written.

The architecture friction point

The agent is given a service account so it can complete its work, and it now acts with more authority than any human who invokes it. An intern's request and an administrator's request reach the same powerful identity.

What HIPAA specifically requires

HIPAA holds the covered entity responsible for PHI wherever it flows. A model provider without a signed BAA is not a permissible destination, and 'the prompt only contained a little PHI' is not a defence — the minimum necessary standard is itself a control.

The artifact that satisfies it is a de-identification record per request plus the BAA chain. The way teams most often fail it: PHI reaching a subprocessor with no BAA, via a logging sidecar nobody mapped.

Implementation artifact — Delegated authority as an intersection, with expiry

Standard-library Python, no external dependencies, runs as written. Executed by the publish gate: if it raises, this page does not ship. Wire it behind REST over HTTPS; the failure mode it guards against is a retried POST creating a duplicate record. The output you hand the assessor is the minimum-necessary de-identification log.

"""Delegated authority: an agent never exceeds the user it acts for.

The failure: an agent is given a service account so it can "do its job", and it
then acts with more authority than any user who invokes it. Correct delegation
is an intersection — the agent may do only what BOTH its own grant and the
invoking user permit — and it must be time-boxed, because a standing delegation
is a standing privilege.
"""
from dataclasses import dataclass


@dataclass(frozen=True)
class Grant:
    subject: str
    permissions: frozenset
    expires_at: int

    def valid(self, now: int) -> bool:
        return now < self.expires_at


class DelegationError(PermissionError):
    pass


class DelegatedAuthority:
    """Effective permissions = user ∩ agent grant, never a union, and never
    the agent's own service identity."""

    def __init__(self):
        self.users: dict[str, frozenset] = {}
        self.grants: dict[str, Grant] = {}
        self.audit: list[dict] = []

    def define_user(self, user: str, permissions: set) -> None:
        self.users[user] = frozenset(permissions)

    def delegate(self, agent: str, permissions: set, expires_at: int) -> Grant:
        g = Grant(agent, frozenset(permissions), expires_at)
        self.grants[agent] = g
        return g

    def effective(self, agent: str, user: str, now: int) -> frozenset:
        g = self.grants.get(agent)
        if g is None:
            raise DelegationError(f"no grant for agent {agent!r}")
        if not g.valid(now):
            raise DelegationError(f"grant for {agent!r} expired")
        if user not in self.users:
            raise DelegationError(f"unknown principal {user!r}")
        return g.permissions & self.users[user]

    def authorise(self, agent: str, user: str, action: str, now: int) -> bool:
        try:
            allowed = self.effective(agent, user, now)
        except DelegationError as exc:
            self.audit.append({"agent": agent, "user": user, "action": action,
                               "allowed": False, "reason": str(exc)})
            return False
        ok = action in allowed
        self.audit.append({"agent": agent, "user": user, "action": action,
                           "allowed": ok,
                           "reason": "" if ok else "outside the intersection"})
        return ok

    def chain(self, agent_a: str, agent_b: str, user: str, now: int) -> frozenset:
        """A delegating to B cannot widen authority — chaining intersects
        again, which is what stops escalation through a hop."""
        return self.effective(agent_a, user, now) & self.grants[agent_b].permissions


if __name__ == "__main__":
    da = DelegatedAuthority()
    da.define_user("analyst", {"read_reports", "read_pii"})
    da.define_user("intern", {"read_reports"})
    da.delegate("summariser", {"read_reports", "read_pii", "delete_records"},
                expires_at=100)

    assert da.authorise("summariser", "analyst", "read_pii", now=1) is True
    # The intern cannot read PII, so neither can an agent acting for them.
    assert da.authorise("summariser", "intern", "read_pii", now=1) is False
    # Nobody granted delete to a user, so the agent's own grant cannot supply it.
    assert da.authorise("summariser", "analyst", "delete_records", now=1) is False

    eff = da.effective("summariser", "intern", now=1)
    assert eff == frozenset({"read_reports"}), eff

    # Expiry is enforced, not advisory.
    assert da.authorise("summariser", "analyst", "read_reports", now=101) is False
    assert "expired" in da.audit[-1]["reason"]

    # Chaining must not widen authority.
    da.delegate("exporter", {"read_reports", "export"}, expires_at=100)
    chained = da.chain("summariser", "exporter", "analyst", now=1)
    assert chained == frozenset({"read_reports"}), chained
    assert "export" not in chained, "chaining widened authority"

    assert da.authorise("unknown_agent", "analyst", "read_reports", now=1) is False

    print("Delegated authority intersection: OK")
    print(f"  audit entries {len(da.audit)}, "
          f"denials {sum(1 for a in da.audit if not a['allowed'])}")

The HIPAA control, as code

Minimum-necessary de-identification with a BAA-pinned egress gate. This is the artifact an assessor asks for under HIPAA specifically — it is not the same control as the one above, and a system that implements one does not thereby implement the other. It executes under the same publish gate.

"""Minimum-necessary de-identification with a BAA-pinned destination gate.

HIPAA holds the covered entity responsible for PHI wherever it flows, so the
control is not "we told people not to paste PHI". Two things must be
structural: PHI is reduced to the minimum necessary BEFORE egress, and the
destination set is pinned to those under a signed BAA, failing closed on
anything else.

Safe Harbor (45 CFR 164.514(b)(2)) lists 18 identifier classes. This implements
the mechanical subset and records a per-request de-identification receipt,
because the auditor asks for proof per request, not a policy document.
"""
import re

SAFE_HARBOR_PATTERNS = {
    "name_mrn": re.compile(r"\bMRN[:\s#]*([A-Z0-9-]{4,})", re.I),
    "ssn": re.compile(r"\b\d{3}-\d{2}-\d{4}\b"),
    "phone": re.compile(r"\b(?:\+1[-.\s]?)?\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}\b"),
    "email": re.compile(r"\b[\w.+-]+@[\w-]+\.[\w.]+\b"),
    "date_full": re.compile(r"\b\d{1,2}/\d{1,2}/(19|20)\d{2}\b"),
    "member_id": re.compile(r"\b(?:member|policy)\s*(?:id|#)[:\s]*([A-Z0-9-]{5,})", re.I),
}


class BAARegistry:
    """Destinations are permissible only as attested data, never by convention."""

    def __init__(self):
        self._signed: dict[str, str] = {}

    def attest(self, destination: str, agreement_ref: str) -> None:
        self._signed[destination] = agreement_ref

    def covered(self, destination: str) -> bool:
        return destination in self._signed

    def reference(self, destination: str) -> str | None:
        return self._signed.get(destination)


class PHIEgressGate:
    def __init__(self, registry: BAARegistry):
        self.registry = registry
        self.receipts: list[dict] = []

    def deidentify(self, text: str) -> tuple[str, dict[str, int]]:
        counts: dict[str, int] = {}
        out = text
        for label, pattern in SAFE_HARBOR_PATTERNS.items():
            out, n = pattern.subn(f"[REDACTED:{label}]", out)
            if n:
                counts[label] = n
        return out, counts

    def send(self, text: str, destination: str) -> dict:
        """Refuses rather than redacting-and-hoping when the BAA is absent."""
        redacted, counts = self.deidentify(text)
        phi_present = bool(counts)
        if phi_present and not self.registry.covered(destination):
            receipt = {"destination": destination, "admitted": False,
                       "reason": "no BAA on file for a PHI-classified payload",
                       "identifier_classes": sorted(counts)}
            self.receipts.append(receipt)
            raise PermissionError(receipt["reason"])
        receipt = {
            "destination": destination,
            "admitted": True,
            "baa_ref": self.registry.reference(destination),
            "identifier_classes": sorted(counts),
            "redactions": sum(counts.values()),
            "payload": redacted,
        }
        self.receipts.append(receipt)
        return receipt


if __name__ == "__main__":
    reg = BAARegistry()
    reg.attest("azure-openai-us-east", "BAA-2026-0041")
    gate = PHIEgressGate(reg)

    note = ("Patient MRN: 88213A, contact 555-867-5309 or a.patient@example.com, "
            "DOB 04/11/1974, follow-up scheduled.")
    ok = gate.send(note, "azure-openai-us-east")
    assert ok["admitted"] and ok["redactions"] >= 4, ok
    assert "88213A" not in ok["payload"] and "555-867-5309" not in ok["payload"], ok
    assert "a.patient@example.com" not in ok["payload"], ok

    try:
        gate.send(note, "some-vendor-eval-endpoint")
        raise AssertionError("PHI reached a destination with no BAA")
    except PermissionError:
        pass

    # No PHI means no BAA requirement — the gate must not over-block.
    benign = gate.send("Summarise ward occupancy trends.", "some-vendor-eval-endpoint")
    assert benign["admitted"] and benign["redactions"] == 0, benign

    print("HIPAA minimum-necessary egress gate: OK")
    print(f"  receipts {len(gate.receipts)}, "
          f"refusals {sum(1 for r in gate.receipts if not r['admitted'])}")

The blueprint

Intersecting Delegated Authority — the request path, with the decision points that must exist before the first model call:

flowchart LR
    USER[Invoking user<br/>entitlements] --> INT{Intersect}
    GRANT[Agent grant<br/>time-boxed] --> INT
    INT --> EFF[Effective permissions]
    EFF --> ACT{Action in effective set?}
    ACT -->|no| DENY[Deny + audit reason]
    ACT -->|yes| DO[Execute as the user, not the agent]
    EFF --> HOP[Delegate to agent B] --> INT2{Intersect again} --> EFF2[Narrower still]

The parts you have to build

1. Principal entitlements — What the human may do, from the system of record.
2. Agent grant — What the agent may ever do, scoped per task.
3. Intersection at call time — Effective = user ∩ grant, computed per request.
4. Time-boxed grants — Expiry enforced, so delegation is not standing authority.
5. Chain intersection — Agent-to-agent delegation intersects again; a hop cannot widen.
6. Denial audit — Every denial recorded with the reason — the escalation signal.

Risk and control matrix

Each row carries an acceptance parameter rather than an adjective, because "low latency" cannot be signed off. Retention here is bound by per the data class retention schedule, enforced automatically.

What the auditor will ask

• Which destinations hold a BAA, and what structurally prevents PHI from reaching one that does not?
  Destinations carry a BAA flag as attested data, and the routing gate refuses a PHI-classified payload to any destination without it. The refusal is logged with its reason.
• If an intern invokes the agent, can it read data only an analyst may see?
  No. Effective permissions are the intersection of the agent's grant and the intern's entitlements, so anything the intern lacks is unavailable regardless of the agent's own grant.
• What authority does the agent have when nobody has invoked it?
  None that matters. The grant is time-boxed and only becomes effective when intersected with an invoking principal, so there is no standing authority to borrow.
• Can agent A delegate to agent B and end up with more permissions than A had?
  No. Chaining intersects again, so each hop can only narrow the set. Widening through a hop is the escalation path this design exists to close.
• How quickly does a revoked entitlement take effect for an in-flight agent?
  Within the entitlement cache TTL, which is bounded by the revocation SLO. The stale-grant window is documented rather than assumed to be zero.
• What is recorded when an agent attempts something outside its effective set?
  The agent, the invoking user, the attempted action and the reason for denial. Repeated denials are the signal that something is probing for authority it does not have.

Related architectures

• Part of enterprise ai compliance architecture.
• A different failure mode of the same component: HIPAA model release gate and golden set evaluation for enterprise AI.
• Where this interacts with another regime, see HIPAA vendor evaluation criteria for enterprise AI implementation.
• Where this interacts with another regime, see HIPAA tracing and token accounting architecture for enterprise LLM.
• Where this interacts with another regime, see HIPAA retrieval architecture with citation integrity for enterprise LLM.
• If this is the blocker in front of you: enterprise AI infrastructure review.