Lasso Security

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.

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 API	Purpose	Gateway operation
`POST /classify`	Score prompt or completion; return `BLOCK` / `WARN` findings	Validate
`POST /classifix`	Apply masks or rewritten text when Lasso provides remediation spans	Mutate

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.

How it works

The gateway POSTs an OpenAI-shaped requestBody (input) or requestBody + responseBody (output) to your wrapper URL.
The wrapper extracts user/assistant text and calls Lasso API v3 with your LASSO_API_KEY.
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.

Response contract

HTTP	Body	Meaning
`200`	`{"verdict": true}`	Allow
`200`	`{"verdict": false, "message": "..."}`	Block (policy)
`200`	`{"verdict": true, "transformed": bool, "result": {...}}`	Mutate
`5xx`	error JSON	Wrapper or Lasso failure

Policy blocks must use 2xx + verdict: false, not HTTP 4xx. See Custom guardrail response contract.

Wrapper endpoints

Path	Operation	Target
`/lasso-classify`	Validate	Request (input)
`/lasso-classify-output`	Validate	Response (output)
`/lasso-classifix`	Mutate	Request
`/lasso-classifix-output`	Mutate	Response

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.

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.

Setup

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).

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.

Deploy on TrueFoundry (optional)

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

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:

Field	Value
Name	`lasso-validate-guardrail`
Operation	Validate
Target	Request
Enforcing Strategy	Enforce
URL	`https://<host>/lasso-classify`
Headers	`Authorization` → `Bearer <WRAPPER_API_KEY>`
Config	`{}`

TrueFoundry custom guardrail form: Validate, Request target, /lasso-classify URL, Authorization Bearer header — Custom Guardrail configuration (input validate)

Name (example)	Operation	Target	Path
`lasso-classify-output`	Validate	Response	`/lasso-classify-output`
`lasso-classifix-input`	Mutate	Request	`/lasso-classifix`
`lasso-classifix-output`	Mutate	Response	`/lasso-classifix-output`

Auth Data → Custom Bearer Auth works the same as Headers if you prefer not to set headers manually.

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.

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.

Troubleshooting

Symptom	Likely cause
`401` from wrapper	`WRAPPER_API_KEY` on the service does not match the dashboard Bearer token
Lasso console shows violation, gateway allows	Finding is `WARN` only; raise to `BLOCK` in Lasso, or use validate rails
Mutate blocks instead of masking	Lasso returned BLOCK without mask spans; use classify for hard stops
Gateway allows despite `verdict: false`	Tenant gateway not honoring verdict-on-200; set Enforce or upgrade gateway

Reference

Item	Value
Source repo	`truefoundry/integrations-custom-guardrails/integrations/lasso-security`
Lasso platform	lasso.security (API key)
Lasso API base	`https://server.lasso.security/gateway/v3`
Selector	`lasso-security/<config-name>`

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What is Lasso Security?

How it works

Response contract

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Troubleshooting

Reference

​What is Lasso Security?

​How it works

​Response contract

​Wrapper endpoints

​Prerequisites

​Setup

​Troubleshooting

​Reference

What is Lasso Security?

How it works

Response contract

Wrapper endpoints

Prerequisites

Setup

Troubleshooting

Reference