LangChain Enterprise RBAC (Python)

Overview

A B2B SaaS team shipped their first RAG feature for two tenants. The factory code looked innocent: build PineconeVectorStore once at module import with namespace="acme-corp" (the first tenant), convert it to a retriever, store it in a module global, reuse on every request. Six weeks later tenant "Initech" went live. Their first search returned three documents from Acme Corp.

The singleton retriever had captured the Acme namespace at process start. RunnableConfig.configurable["tenant_id"] was being passed in — but the retriever never read it, because the filter was baked in. Every request for every tenant hit the same Pinecone namespace. Security review caught it three days later and put a hold on the SOC2 renewal. This is pain-catalog entry P33, the single most common cause of cross-tenant leak in LangChain 1.0 production.

This skill fixes it with four workstreams:

• P33 — retriever-per-request factory — build the retriever inside the chain or agent invocation, keyed by tenant_id from RunnableConfig. Never at module scope. Unit-test with two tenants and assert non-overlap.
• Role-scoped tool allowlist — build the agent per-request with only the tools the current user's role permits. Forbidden tools are not passed to create_agent at all, so the model cannot call them even if it tries.
• Per-tenant rate limit + budget — scope the InMemoryRateLimiter (or a Redis-backed equivalent) by tenant_id, and check a per-tenant USD budget before invoking the model.
• Structured audit log — JSON log with user_id, tenant_id, chain_name, tools_called, cost_usd, outcome, emitted in both success and failure paths. Ships to SIEM or BigQuery.

Two failure patterns anchor this skill: import-time retriever binding (P33) and missing audit log on tool failure (the try block logs on success but the except branch re-raises without emitting, so incident response has no record of denied tool calls). Pinned: langchain-core 1.0.x, langgraph 1.0.x, langchain-anthropic 1.0.x, langchain-openai 1.0.x, langchain-postgres 0.0.15+ (for PGVector RLS), pinecone-client 5.x, chromadb 0.5.x. Pain-catalog anchors: P33 primary, P18, P24, P31, P37.

Prerequisites

• Python 3.10+
• langchain-core >= 1.0, < 2.0, langgraph >= 1.0, < 2.0
• At least one vector-store backend: pinecone-client, langchain-postgres (PGVector), chromadb, or faiss-cpu (single-tenant only — see §Step 2)
• A structured logging sink: stdout JSON for local, Cloud Logging / Datadog / Splunk HEC / BigQuery streaming insert for production
• A tenant authorization claim in every request (JWT tid claim, session cookie, or header — the auth boundary is out of scope for this skill but assumed correct)

Instructions

Step 1 — Build the retriever per-request, never at import

Move retriever construction inside the chain or agent invocation, keyed by config["configurable"]["tenant_id"].

from langchain_core.runnables import RunnableConfig, RunnableLambda
from langchain_pinecone import PineconeVectorStore

# WRONG — retriever bound at import time with first tenant's namespace.
# RETRIEVER = PineconeVectorStore(index_name="rag", namespace="acme-corp",
#     embedding=emb).as_retriever(search_kwargs={"k": 4})

# RIGHT — factory called per-request, reads tenant from RunnableConfig.
def retriever_for(config: RunnableConfig):
    tenant_id = config["configurable"]["tenant_id"]  # required, no default
    if not tenant_id:
        raise PermissionError("tenant_id missing from RunnableConfig")
    store = PineconeVectorStore(
        index_name="rag",
        namespace=tenant_id,   # P33 fix — namespace per-invocation
        embedding=emb,
    )
    return store.as_retriever(search_kwargs={"k": 4})

def retrieve(inputs: dict, config: RunnableConfig):
    return retriever_for(config).invoke(inputs["query"])

chain = RunnableLambda(retrieve) | prompt | model
result = chain.invoke({"query": "..."},
    config={"configurable": {"tenant_id": "initech"}})

No default on tenant_id — a missing tenant must be a hard error, not a silent fallback. See Retriever-per-request for factory lifecycle and PGVector RLS / Chroma / FAISS adapters.

Step 2 — Pick a vector-store isolation primitive

Store	Isolation primitive	Per-tenant latency	Max tenants	Safety notes
Pinecone	namespace=tenant_id per query	~40ms p50 (shared index)	100,000+ per index	Namespace is the documented isolation boundary; still apply metadata {"tenant_id": tid} as defense in depth
PGVector	Postgres row-level security (RLS) on tenant_id column	~20ms p50 (HNSW index)	Bounded by Postgres row count	Use SET LOCAL app.tenant_id = :tid per transaction; RLS policy USING (tenant_id = current_setting('app.tenant_id'))
Chroma	Collection-per-tenant (get_or_create_collection(name=tid))	~30ms p50	~1,000 before metadata overhead	Good isolation at small scale; collection creation is synchronous — provision lazily but cache the handle per-request
FAISS	In-process index-per-tenant	~5ms p50 (in-memory)	10-50 practical limit	Poor fit for multi-tenant SaaS — cannot shard across processes, reloads on every deploy, no durable filter. Use for single-tenant evaluation only

Pinecone scales highest. PGVector with RLS is the strongest primitive when isolation must be auditable at the database layer (RLS is enforced by the server even if application code is bypassed). Chroma is fine for ≤1,000 tenants. FAISS is not a multi-tenant production choice — document so future engineers do not adopt it. See Vector-store isolation for the PGVector RLS DDL and Chroma lifecycle.

Step 3 — Build the agent per-request with a role-scoped tool allowlist

Never bind every tool to every agent and trust the model to pick the right one. Build the agent inside the request handler with only the tools the user's role permits.

from langgraph.prebuilt import create_agent

# Map role -> allowed tool names. Owned by IAM config, not the skill.
ROLE_TOOLS: dict[str, set[str]] = {
    "viewer": {"search_docs"},
    "editor": {"search_docs", "create_note"},
    "admin":  {"search_docs", "create_note", "delete_note", "export_audit"},
}
ALL_TOOLS = {t.name: t for t in [search_docs, create_note, delete_note, export_audit]}

def agent_for(user_role: str, tenant_id: str):
    allowed = ROLE_TOOLS.get(user_role, set())
    tools = [ALL_TOOLS[n] for n in allowed if n in ALL_TOOLS]
    # Forbidden tools are not passed in — the model never sees them.
    return create_agent(model, tools=tools)

agent = agent_for(user_role="viewer", tenant_id="initech")
# viewer has no delete_note -> the agent cannot call it.

Add a denylist for dangerous argument patterns (SQL with DROP / TRUNCATE, shell with rm -rf / sudo, URLs to internal metadata endpoints) via a pre_model_hook or tool wrapper — allowlist bounds which tools run, denylist bounds what arguments they accept. See Role-scoped tool allowlist.

Step 4 — Scope rate limits and budgets by tenant

Per-tenant limits prevent one tenant's runaway job from exhausting shared model capacity. Rate-limit detail is covered in langchain-rate-limits; cost-budget detail in langchain-cost-tuning. The only RBAC-specific requirement here: limiter key must include tenant_id — never a process-global singleton.

# Sketch only — see langchain-rate-limits for production implementation.
_limiters: dict[str, InMemoryRateLimiter] = {}

def limiter_for(tenant_id: str) -> InMemoryRateLimiter:
    if tenant_id not in _limiters:
        # Tier lookup — different plans get different budgets.
        rps = TENANT_TIER_LIMITS.get(tenant_id, 1.0)  # 1.0 rps = free-tier default
        _limiters[tenant_id] = InMemoryRateLimiter(requests_per_second=rps)
    return _limiters[tenant_id]

For multi-process deployments use a Redis-backed limiter — InMemoryRateLimiter is per-process only, so 1 rps × 8 workers = 8 rps aggregate.

Step 5 — Emit a structured audit log on every invocation

The audit log is the record of truth during an incident. Emit on both success and failure paths. The common bug is logging in the try block only — when a tool raises, the except branch re-raises without emitting, so the incident responder has no record of the denied call.

import json
import time
import uuid
from contextlib import contextmanager

@contextmanager
def audit(ctx: dict):
    started = time.monotonic()
    trace_id = str(uuid.uuid4())
    record = {**ctx, "trace_id": trace_id, "outcome": "pending"}
    try:
        yield record
        record["outcome"] = record.get("outcome", "success")
    except Exception as exc:
        record["outcome"] = "error"
        record["error_class"] = type(exc).__name__
        record["error_message"] = str(exc)[:500]  # truncate — no PII leakage
        raise
    finally:
        record["latency_ms"] = int((time.monotonic() - started) * 1000)  # 1000 ms per second
        print(json.dumps(record))  # or a SIEM / BigQuery client

ctx = {
    "user_id": "u_42",
    "tenant_id": "initech",
    "chain_name": "rag-qa-v3",
    "role": "viewer",
}
with audit(ctx) as record:
    result = chain.invoke(inputs, config={"configurable": ctx})
    record["tools_called"] = [m.name for m in result.get("tool_calls", [])]
    record["input_tokens"]  = result["usage"]["input_tokens"]
    record["output_tokens"] = result["usage"]["output_tokens"]
    record["cost_usd"]      = cost_of(result["usage"])

The try / finally pattern guarantees emission even when the chain raises. Required fields: user_id, tenant_id, chain_name, outcome, latency_ms, trace_id. Recommended: tools_called, input_tokens, output_tokens, cost_usd, role. See Audit-log schema for the full catalog, JSON example, SIEM / BigQuery ingestion, and query recipes.

Step 6 — Two-tenant regression test for cross-tenant leak

The test that would have caught P33 on day one. Seed two tenants with distinct documents, run a golden query as each, assert non-overlap on retrieved IDs.

import pytest

@pytest.fixture
def two_tenant_store():
    seed("acme",    ["acme-doc-1",    "acme-doc-2"])
    seed("initech", ["initech-doc-1", "initech-doc-2"])
    yield
    cleanup(["acme", "initech"])

def test_tenant_isolation(two_tenant_store):
    acme_hits    = chain.invoke({"query": "q"}, config={"configurable": {"tenant_id": "acme"}})
    initech_hits = chain.invoke({"query": "q"}, config={"configurable": {"tenant_id": "initech"}})
    acme_ids    = {d.id for d in acme_hits["documents"]}
    initech_ids = {d.id for d in initech_hits["documents"]}
    assert acme_ids.isdisjoint(initech_ids), \
        f"CROSS-TENANT LEAK: overlap={acme_ids & initech_ids}"
    assert all("acme"    in doc_id for doc_id in acme_ids)
    assert all("initech" in doc_id for doc_id in initech_ids)

Run in CI on every PR. A regression to import-time retriever binding fails immediately. See Multi-tenant regression tests for fixtures covering tool-allowlist violation, audit-log completeness, and rate-limiter scoping.

Output

• Retriever factory keyed by RunnableConfig.configurable["tenant_id"]
• Vector-store choice made against the 4-row isolation table, not by defaults
• Agent constructed per-request with a role-scoped tool allowlist (not a deny-all at tool-call time)
• Rate limiter and cost budget keyed by tenant_id, never a process global
• Structured audit log emitted on both success and failure paths with required fields (user_id, tenant_id, chain_name, outcome, latency_ms, trace_id)
• Two-tenant pytest fixture in CI that asserts cross-tenant non-overlap

Error Handling

Error / symptom	Cause	Fix
Tenant A's docs returned to Tenant B after deploy	Singleton retriever bound at import (P33)	Move to per-request factory keyed by config["configurable"]["tenant_id"] (Step 1)
KeyError: 'tenant_id' in retriever factory	Caller forgot to pass configurable	Fail fast with PermissionError; never default to a tenant
permission denied for relation documents on PGVector	RLS policy enabled but session variable not set	SET LOCAL app.tenant_id = :tid inside the transaction
Agent calls a tool the user's role should not have	Every tool bound at agent construction	Build agent per-request with only role-permitted tools (Step 3)
Audit log missing entries for errored invocations	Log emitted inside try only, not finally	Move emit to finally block (Step 5)
Shared rate limit trips all tenants when one misbehaves	Process-global InMemoryRateLimiter	Key limiter by tenant_id; use Redis-backed for multi-process (Step 4)
Cross-tenant leak regression ships to prod	No two-tenant CI test	Add the Step 6 fixture; run on every PR
Audit log contains raw PII from prompts	Logging inputs verbatim	Log field names / token counts / IDs only; never log raw message content

Examples

Full multi-tenant RAG agent, end-to-end

Combines all six steps: retriever-per-request, Pinecone namespace isolation, role-scoped tools, per-tenant rate limit, audit-log context manager, regression test. Assembly is ~80 lines. See Retriever-per-request.

Migrating from a shared singleton to per-request

Wrap the old singleton, add the factory alongside, route by feature flag, ship the regression test first, flip the flag, delete the singleton. Typical migration window: 1-2 sprints. See Multi-tenant regression tests.

Exporting audit log to BigQuery for compliance queries

Stream each record to BigQuery per the Audit-log schema. Recipes: "tool calls by user X in last 24h", "tenants with >1% error rate", "highest-spend tenants".

Resources

• LangChain Python: RunnableConfig
• LangChain Python: Multiple retrievers
• LangGraph: create_agent
• Pinecone: Namespaces
• PGVector: Row-level security
• SOC2 CC6.1 — logical access controls
• Pack pain catalog: docs/pain-catalog.md (primary P33; adjacent P18, P24, P31, P37)
• Sibling skills: langchain-rate-limits (per-tenant limiters), langchain-cost-tuning (per-tenant budgets), langchain-security-basics (input redaction upstream of audit log)