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Deploy the integrations/lasso-security FastAPI wrapper on any public HTTPS host. The gateway calls it at llm_input / llm_output via the Custom Guardrail contract; the wrapper forwards traffic to Lasso API v3 and returns verdict JSON on HTTP 200.

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What is Lasso Security?

Lasso Security is a SaaS platform for classifying and remediating LLM traffic. You define deputies and policies in the Lasso platform; the wrapper does not embed policy logic. API v3 exposes two operations used by this integration:
Lasso APIPurposeGateway operation
POST /classifyScore prompt or completion; return BLOCK / WARN findingsValidate
POST /classifixApply masks or rewritten text when Lasso provides remediation spansMutate
The wrapper sets messageType=PROMPT for input hooks and messageType=COMPLETION for output hooks. Optional sessionId / userId from gateway context are forwarded when present for conversation-aware policy.

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How it works

  1. The gateway POSTs an OpenAI-shaped requestBody (input) or requestBody + responseBody (output) to your wrapper URL.
  2. The wrapper extracts user/assistant text and calls Lasso API v3 with your LASSO_API_KEY.
  3. The wrapper returns HTTP 200 with a policy outcome in the body (see below). Infrastructure failures return HTTP 5xx.
On validate rails, only findings with action: BLOCK produce {"verdict": false}; WARN-only findings are logged and allowed. On mutate rails, when Lasso returns mask metadata or rewritten content, the wrapper returns {"verdict": true, "transformed": true, "result": {...}} so the gateway can replace the request or response. Hard blocks without mask data still return verdict: false.

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Response contract

HTTPBodyMeaning
200{"verdict": true}Allow
200{"verdict": false, "message": "..."}Block (policy)
200{"verdict": true, "transformed": bool, "result": {...}}Mutate
5xxerror JSONWrapper or Lasso failure
Policy blocks must use 2xx + verdict: false, not HTTP 4xx. See Custom guardrail response contract.

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Wrapper endpoints

PathOperationTarget
/lasso-classifyValidateRequest (input)
/lasso-classify-outputValidateResponse (output)
/lasso-classifixMutateRequest
/lasso-classifix-outputMutateResponse
GET /health — health check. GET /debug/runtime-config — bearer-gated deploy verification. All POST routes expect Authorization: Bearer <WRAPPER_API_KEY> when the key is configured on the wrapper.

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Prerequisites

  • Lasso API key from the Lasso Security platform, plus deputies configured for your policies.
  • Public HTTPS URL for the deployed wrapper.
  • WRAPPER_API_KEY — shared secret; the gateway sends it as Authorization: Bearer … when calling the wrapper.

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Setup

1

Clone and configure

git clone https://github.com/truefoundry/integrations-custom-guardrails
cd integrations-custom-guardrails/integrations/lasso-security
cp .env.example .env
.env
LASSO_API_KEY=<from https://www.lasso.security/>
WRAPPER_API_KEY=<generate: python -c "import secrets; print(secrets.token_urlsafe(32))">
Get LASSO_API_KEY in the Lasso Security platform. Default API base: https://server.lasso.security/gateway/v3 (override with LASSO_API_BASE if needed).
2

Deploy the wrapper

Docker:
docker build -t lasso-guardrails-tfy .
docker run --rm -p 8000:8000 --env-file .env lasso-guardrails-tfy
Local:
pip install -r requirements.txt
uvicorn main:app --host 0.0.0.0 --port 8000
Put TLS in front of the service (load balancer, ingress, or your platform’s HTTPS URL). The gateway must reach paths such as https://<host>/lasso-classify.
Set TFY_WORKSPACE_FQN, TFY_PUBLIC_HOST, TFY_PUBLIC_PATH, and secret FQNs in .env. Create secrets lasso-api-key and wrapper-api-key under group lasso-guardrails-tfy in Platform → Secrets, then:
pip install -U truefoundry
tfy login
python deploy.py --wait
3

Register Custom Guardrail configs

AI Gateway → Guardrails → + Add New Guardrails Group → type Custom.
  • Group name: lasso-security
  • Add one config per wrapper path (four total), or start with input validate only.
Input validate example:
FieldValue
Namelasso-validate-guardrail
OperationValidate
TargetRequest
Enforcing StrategyEnforce
URLhttps://<host>/lasso-classify
HeadersAuthorization → Bearer <WRAPPER_API_KEY>
Config{}
TrueFoundry custom guardrail form: Validate, Request target, /lasso-classify URL, Authorization Bearer header
Register the remaining configs:
Name (example)OperationTargetPath
lasso-classify-outputValidateResponse/lasso-classify-output
lasso-classifix-inputMutateRequest/lasso-classifix
lasso-classifix-outputMutateResponse/lasso-classifix-output
Auth Data → Custom Bearer Auth works the same as Headers if you prefer not to set headers manually.
4

Attach to traffic

Model pin: AI Gateway → Models → <model> → Guardrails → attach group lasso-security.Per request — X-TFY-GUARDRAILS header, selector format <group>/<config-name>:
{
  "llm_input_guardrails": ["lasso-security/lasso-validate-guardrail"],
  "llm_output_guardrails": ["lasso-security/lasso-classify-output"]
}
For PII masking, use the lasso-classifix-* config names instead of classify.
5

Verify

Call the wrapper directly:
curl -sS https://<host>/lasso-classify \
  -H "Authorization: Bearer $WRAPPER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "requestBody": {"messages": [{"role": "user", "content": "My email is jane@example.com"}]},
    "context": {"user": {"subjectSlug": "test-user"}}
  }'
Expect {"verdict": false, ...} when a deputy BLOCKs, or {"verdict": true} when allowed (depends on your Lasso policy).
curl -sS https://<host>/debug/runtime-config -H "Authorization: Bearer $WRAPPER_API_KEY"
Confirm lasso_api_key_configured: true and the routes map.

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Troubleshooting

SymptomLikely cause
401 from wrapperWRAPPER_API_KEY on the service does not match the dashboard Bearer token
Lasso console shows violation, gateway allowsFinding is WARN only; raise to BLOCK in Lasso, or use validate rails
Mutate blocks instead of maskingLasso returned BLOCK without mask spans; use classify for hard stops
Gateway allows despite verdict: falseTenant gateway not honoring verdict-on-200; set Enforce or upgrade gateway

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Reference

ItemValue
Source repotruefoundry/integrations-custom-guardrails/integrations/lasso-security
Lasso platformlasso.security (API key)
Lasso API basehttps://server.lasso.security/gateway/v3
Selectorlasso-security/<config-name>