diff --git a/DEPLOYMENT.md b/DEPLOYMENT.md
index dc84d19..bee7a1b 100644
--- a/DEPLOYMENT.md
+++ b/DEPLOYMENT.md
@@ -34,14 +34,79 @@ psql -c "GRANT ALL PRIVILEGES ON DATABASE candle_annotator TO ml_user;"
 
 #### Environment Configuration
 
-Create a `.env` file in the project root:
+Create a `.env` file in the project root based on `.env.example`:
+
+```bash
+cp .env.example .env
+```
+
+Edit `.env` to customize:
 
 ```env
 DATABASE_URL=postgresql://ml_user:ml_password@localhost:5432/candle_annotator
 NODE_ENV=development
 PORT=3000
+
+# Authentication (Auth.js v5)
+AUTH_SECRET=your_strong_random_secret_here
+AUTH_TRUST_HOST=true
+
+# Google OAuth
+AUTH_GOOGLE_ID=your_google_oauth_client_id
+AUTH_GOOGLE_SECRET=your_google_oauth_client_secret
+
+# Default admin user
+DEFAULT_ADMIN_EMAIL=admin@example.com
+DEFAULT_ADMIN_PASSWORD=your_strong_password_here
 ```
 
+#### Google OAuth Setup
+
+To enable Google OAuth sign-in:
+
+1. **Create a Google OAuth Application**:
+   - Go to [Google Cloud Console](https://console.cloud.google.com/)
+   - Create a new project
+   - Enable the "Google+ API"
+   - Go to "Credentials" and click "Create Credentials" → "OAuth 2.0 Client IDs"
+   - Select "Web application"
+   - Add authorized redirect URIs:
+     - `http://localhost:3000/api/auth/callback/google` (local development)
+     - `https://yourdomain.com/api/auth/callback/google` (production)
+   - Copy the Client ID and Client Secret
+
+2. **Set Environment Variables**:
+   ```env
+   AUTH_GOOGLE_ID=<your-client-id>
+   AUTH_GOOGLE_SECRET=<your-client-secret>
+   ```
+
+3. **Generate AUTH_SECRET**:
+   ```bash
+   openssl rand -hex 32
+   ```
+
+#### Database Migrations
+
+After setting up the database and environment variables, run the migrations:
+
+1. **Run Drizzle migrations** (creates schema):
+   ```bash
+   npm run db:migrate
+   ```
+
+2. **Run the user migration script** (creates default admin user, backfills user_id):
+   ```bash
+   DEFAULT_ADMIN_EMAIL=admin@example.com \
+   DEFAULT_ADMIN_PASSWORD=your_password \
+   npx tsx scripts/migrate-users.ts
+   ```
+
+   This script:
+   - Creates a default admin user with the specified email and password (hashed with bcryptjs)
+   - Backfills `user_id` on all existing rows in: `charts`, `annotations`, `annotation_types`, `span_annotations`, `span_label_types`
+   - Is idempotent (safe to run multiple times)
+
 #### Run Migrations
 
 Database migrations run automatically on application startup. To run manually:
@@ -159,19 +224,34 @@ PORT=3001 npm run dev
 
 ## Environment Variables
 
-Required environment variables:
+### Required Variables
 
 - `DATABASE_URL` - PostgreSQL connection string (e.g., `postgresql://ml_user:ml_password@localhost:5432/candle_annotator`)
 - `NODE_ENV` - Environment (`development` or `production`)
 - `PORT` - Server port (default: 3000)
+- `AUTH_SECRET` - Random secret for Auth.js JWT signing (generate with `openssl rand -hex 32`)
+- `AUTH_GOOGLE_ID` - Google OAuth Client ID
+- `AUTH_GOOGLE_SECRET` - Google OAuth Client Secret
+- `DEFAULT_ADMIN_EMAIL` - Default admin user email (used by migration script)
+- `DEFAULT_ADMIN_PASSWORD` - Default admin user password (used by migration script)
 
-Optional variables for ML inference:
+### Authentication Variables
+
+- `AUTH_TRUST_HOST` - Set to `true` when using HTTP (localhost development), `false` for HTTPS production with proper domain
+- `AUTH_GOOGLE_ID` - Google OAuth Client ID from Google Cloud Console
+- `AUTH_GOOGLE_SECRET` - Google OAuth Client Secret from Google Cloud Console
+
+### Optional Variables for ML Inference
 
 - `INFERENCE_API_URL` - ML service endpoint (default: `http://localhost:8001`)
 - `INFERENCE_API_TIMEOUT` - Request timeout in ms (default: 30000)
 - `INFERENCE_BATCH_TIMEOUT` - Batch processing timeout in ms (default: 120000)
 - `NEXT_PUBLIC_PREDICTIONS_ENABLED` - Enable predictions UI (default: true)
 
+### API Key Variable
+
+- `API_KEY` - Strong random key for authenticating requests between Next.js and ML service (generate with `openssl rand -hex 32`)
+
 ## File Structure
 
 ```
@@ -406,7 +486,7 @@ docker run -d \
   candle-annotator
 ```
 
-### Environment Configuration
+### Environment Configuration for Docker
 
 Create a `.env` file in the project root based on `.env.example`:
 
@@ -414,11 +494,30 @@ Create a `.env` file in the project root based on `.env.example`:
 cp .env.example .env
 ```
 
-Edit `.env` to customize:
-```
+Edit `.env` to customize for your deployment:
+```env
 NODE_ENV=production
 PORT=3000
 DATABASE_URL=postgresql://ml_user:ml_password@postgres:5432/candle_annotator
+
+# Authentication
+AUTH_SECRET=your_strong_random_secret_here
+AUTH_TRUST_HOST=false
+AUTH_GOOGLE_ID=your_google_oauth_client_id
+AUTH_GOOGLE_SECRET=your_google_oauth_client_secret
+
+# Default admin user
+DEFAULT_ADMIN_EMAIL=admin@example.com
+DEFAULT_ADMIN_PASSWORD=your_strong_password_here
+
+# API Key
+API_KEY=your_strong_random_api_key_here
+
+# ML Inference (optional)
+INFERENCE_API_URL=http://ml-service:8001
+INFERENCE_API_TIMEOUT=30000
+INFERENCE_BATCH_TIMEOUT=120000
+NEXT_PUBLIC_PREDICTIONS_ENABLED=true
 ```
 
 Pass environment variables to docker-compose:
@@ -427,6 +526,8 @@ Pass environment variables to docker-compose:
 docker-compose --env-file .env up -d
 ```
 
+After containers are running, the user migration will run automatically during startup.
+
 ### Data Persistence
 
 The application stores all data in PostgreSQL using the Docker named volume `postgres-data`. This ensures data persists across container restarts:
@@ -664,9 +765,12 @@ For production deployments, consider:
 
 ## Notes
 
-- This application is designed for **single-user local use** only
-- There is no authentication or user management
+- The application now includes **user authentication and multi-user support**
+- Users can sign up with email/password or use Google OAuth
+- A default admin user is created during the migration phase (see Database Migrations section)
+- Each user's data (charts, annotations, etc.) is isolated and scoped by `user_id`
 - PostgreSQL is used for all application data (frontend and ML service)
-- The shared database enables the ML service to directly query candle and annotation data
+- The shared database enables the ML service to directly query candle and annotation data with user scoping
 - Docker deployment provides lightweight containerization ideal for standalone instances
 - The multi-stage Dockerfile keeps image size minimal (~100MB)
+- Auth.js v5 is used for authentication with JWT strategy and 30-day session expiry