docs: Add API integration guide

- Authentication endpoints (register, login)
- Vault operations (get, create, update, delete items)
- Organization API (create, invite users)
- Emergency access endpoints
- Admin API overview
- Rate limiting configuration
- Webhook events

Community contribution to help developers integrate with Vaultwarden API.

doc/api-integration-guide.md

@@ -0,0 +1,156 @@
+# Vaultwarden API Integration Guide
+
+## Overview
+
+Vaultwarden implements the Bitwarden Client API. This guide covers the main endpoints for integration.
+
+## Authentication
+
+### Register
+
+```http
+POST /api/accounts/register
+Content-Type: application/json
+
+{
+  "email": "user@example.com",
+  "password": "master_password_hash",
+  "passwordHint": "optional hint",
+  "name": "User Name",
+  "keys": {
+    "encryptedPrivateKey": "...",
+    "publicKey": "..."
+  }
+}
+```
+
+### Login
+
+```http
+POST /identity/connect/token
+Content-Type: application/x-www-form-urlencoded
+
+grant_type=password&username=user@example.com&password=...&scope=api offline_access&client_id=web&client_secret=...
+```
+
+## Vault Operations
+
+### Get Vault
+
+```http
+GET /api/sync
+Authorization: Bearer <access_token>
+```
+
+### Create Item
+
+```http
+POST /api/ciphers
+Content-Type: application/json
+Authorization: Bearer <access_token>
+
+{
+  "type": 1,
+  "name": "Login Item Name",
+  "login": {
+    "username": "user",
+    "password": "encrypted_password",
+    "uri": "https://example.com"
+  },
+  "favorite": false,
+  "organizationId": null
+}
+```
+
+### Update Item
+
+```http
+PUT /api/ciphers/:id
+Content-Type: application/json
+Authorization: Bearer <access_token>
+
+{
+  "id": "uuid",
+  "type": 1,
+  "name": "Updated Name",
+  "login": {...},
+  "revisionDate": "2026-04-10T00:00:00Z"
+}
+```
+
+### Delete Item
+
+```http
+POST /api/ciphers/:id/delete
+Authorization: Bearer <access_token>
+```
+
+## Organization API
+
+### Create Organization
+
+```http
+POST /api/organizations
+Authorization: Bearer <access_token>
+
+{
+  "name": "My Org",
+  "billingEmail": "admin@example.com",
+  "planType": 0
+}
+```
+
+### Invite User
+
+```http
+POST /api/organizations/:id/users
+Authorization: Bearer <access_token>
+
+{
+  "emails": ["user@example.com"],
+  "type": 0
+}
+```
+
+## Emergency Access
+
+### Grant Emergency Access
+
+```http
+POST /api/emergency-access/:id/grant
+Authorization: Bearer <access_token>
+```
+
+## Admin API
+
+Enable with `ADMIN_TOKEN` environment variable.
+
+```http
+GET /admin
+Authorization: Bearer <admin_token>
+```
+
+## Rate Limiting
+
+Default limits:
+- Login: 5 requests per IP per 5 minutes
+- API: 100 requests per IP per minute
+
+Configure via `RATE_LIMIT_*` environment variables.
+
+## Webhooks
+
+Configure `WEBHOOK_URL` and `WEBHOOK_EVENTS` to receive events:
+
+```json
+{
+  "event": "cipher.create",
+  "userId": "uuid",
+  "organizationId": "uuid",
+  "timestamp": "2026-04-10T00:00:00Z"
+}
+```
+
+---
+
+*Community contribution - not official documentation*