api-integration

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SKILL.md (first lines)

# API Integration Skill

Design integration patterns, webhook flows, event pipelines, and API composition strategies.

---

## Webhook Design

### Outbound Webhook Endpoint (from your system to 3rd party)
```
POST {subscriber_url}
Headers:
  Content-Type: application/json
  X-Webhook-Signature: hmac-sha256=<sig>
  X-Webhook-Event: order.created
  X-Webhook-Delivery: <uuid>
  X-Webhook-Timestamp: <unix-epoch>
```

**Payload envelope**
```json
{
  "event": "order.created",
  "delivery_id": "uuid",
  "created_at": "ISO8601",
  "data": { ... }
}
```

**Signature verification** (receiver side):
```python
import hmac, hashlib
expected = hmac.new(secret.encode(), payload_bytes, hashlib.sha256).hexdigest()
assert f"sha256={expected}" == request.headers["X-Webhook-Signature"]
```

### Inbound Webhook Registration API
```
POST   /api/v1/webhooks           — register subscriber URL + events
GET    /api/v1/webhooks           — list subscriptions
DELETE /api/v1/webhooks/{id}      — unsubscribe
POST   /api/v1/webhooks/{id}/test — fire test event
GET    /api/v1/webhooks/{id}/deliveries — delivery history + status
```

---

## API Chaining / Composition Pattern

```
Step 1: POST /auth/token           → get access_token
Step 2: GET  /api/v1/user/profile  → get user.id (use token from step 1)
Step 3: POST /api/v1/orders        → create order (use user.id from step 2)
Step 4: POST /api/v1/payments      → charge (use order.id from step 3)
```

Always: handle failures at each step independently, use idempotency keys, implement retry with exponential backoff.

---

## Event-Driven Architecture

### Event Schema (CloudEvents spec)
```json
{
  "specversion": "1.0",
  "type": "com.example.order.created",
  "source": "/orders-service",
  "id": "uuid",
  "time": "2024-01-01T00:00:00Z",
  "datacontenttype": "application/json",
  "data": { "order_id": "...", "amount": 99.99 }
}
```

### Topics / Queues design
| Topic | Producers | Consumers | Retention |
|-------|-----------|-----------|-----------|
| `orders.created` | orders-svc | payments-svc, email-svc | 7 days |
| `payments.completed` | payments-svc | orders-svc, ledger-svc | 30 days |
| `users.deleted` | users-svc | all services | 90 days |

---

## Saga Pattern (Distributed Transaction)

```
Choreography saga for order checkout:
1. orders-svc emits order.created
2. inventory-svc reserves stock → emits inventory.reserved
3. payments-svc charges card → emits payment.completed
4. orders-svc emits order.confirmed

On failure at step 3:
← payments-svc emits payment.failed
← inventory-svc releases stock (compensating transaction)
← orders-svc emits order.cancelled
```

---

## Outbox Pattern (reliable event publishing)

```sql
-- Transactional outbox table
CREATE TABLE outbox_events (
  id UUID PRIMARY KEY,
  aggregate_type VARCHAR,
  aggregate_id UUID,
  event_type VARCHAR,
  payload JSONB,
  created_at TIMESTAMP,
  published_at TIMESTAMP NULL
);
-- Write to DB + outbox in same transaction
-- Separate publisher polls outbox and sends to message broker
```

---

From LambdaTest/agent-skills, MIT.

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