authgate

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README

AuthGate

A lightweight OAuth 2.0 Device Authorization Grant server for CLI tools and browserless devices

Security Scanning Lint and Testing License

Table of Contents

Why AuthGate?

The Problem

Modern CLI tools and IoT devices need to access user resources securely, but traditional OAuth 2.0 flows weren't designed for them:

  • Authorization Code Flow requires a browser redirect and a local callback server
  • Client Credentials Flow can't authenticate specific users
  • Password Grant requires users to enter credentials directly into apps (security risk)
  • Embedding client_secret in distributed applications is insecure
Real-World Scenarios
  • 🖥️ CLI tools (like gh, aws-cli) need to access user data
  • 📺 Smart TVs and streaming devices authenticating streaming services
  • 🏠 IoT devices that lack browsers or input capabilities
  • 🤖 CI/CD pipelines and automation scripts requiring user authorization
  • 🎮 Gaming consoles logging into online services
The Solution

Device Authorization Grant (RFC 8628) solves this by splitting the authorization flow:

  1. Device requests a code from the server
  2. User visits a URL on another device (phone/computer) with a browser
  3. User logs in and enters the short code
  4. Device polls the server until authorization is complete
  5. Device receives an access token

AuthGate provides a production-ready implementation of this flow that you can deploy in minutes.

Features

  • ✅ RFC 8628 Compliant - Full implementation of OAuth 2.0 Device Authorization Grant
  • ✅ Lightweight - Single binary, SQLite database, no external dependencies
  • ✅ Easy Configuration - .env file support for all settings
  • ✅ Session-Based Auth - Secure user login with encrypted cookies (7-day expiry)
  • ✅ JWT Tokens - Industry-standard access tokens with HMAC-SHA256 signing
  • ✅ Example CLI - Complete working example of a client implementation
  • ✅ Token Verification - Built-in endpoint to validate tokens (/oauth/tokeninfo)
  • ✅ Health Check - Database connection monitoring via /health endpoint
  • ✅ Graceful Shutdown - Proper signal handling for zero-downtime deployments
  • ✅ Embedded Assets - Templates and static files compiled into binary
  • ✅ Cross-Platform - Runs on Linux, macOS, Windows
  • ✅ Docker Ready - Multi-arch images with security best practices
  • ✅ Static Binaries - CGO-free builds for easy deployment

Quick Start

Prerequisites
  • Go 1.24 or higher
  • Make (optional, but recommended for convenience commands)
Installation
# Clone the repository
git clone <repository-url>
cd authgate

# Copy environment configuration
cp .env.example .env

# Edit .env and set your secrets
nano .env

# Build the server (outputs to bin/authgate with version info)
make build

# Or build directly with Go
go build -o bin/authgate .
Run the Server
# Show version information
./bin/authgate -v
./bin/authgate --version

# Show help
./bin/authgate -h

# Start the server
./bin/authgate server

# Or directly with Go
go run . server

The server will start on http://localhost:8080 by default.

Important: Note the client_id printed in the startup logs - you'll need this for the CLI example.

Docker Deployment

AuthGate provides multi-architecture Docker images for easy deployment:

# Build for your platform
make build_linux_amd64  # For Linux x86_64
make build_linux_arm64  # For Linux ARM64

# Build Docker image (with version tag)
docker build -f docker/Dockerfile \
  --build-arg VERSION=v1.0.0 \
  -t authgate:v1.0.0 \
  -t authgate:latest \
  .

# Or build without version (defaults to "dev")
docker build -f docker/Dockerfile -t authgate .

# Run with Docker
docker run -d \
  --name authgate \
  -p 8080:8080 \
  -v authgate-data:/app/data \
  -e JWT_SECRET=your-secret-here \
  -e SESSION_SECRET=your-session-secret \
  -e BASE_URL=http://localhost:8080 \
  authgate

# Check health
curl http://localhost:8080/health

# Inspect image labels to verify version
docker inspect authgate:v1.0.0 | grep -A 5 Labels
Docker Features
  • Alpine-based (minimal attack surface)
  • Multi-architecture support (amd64, arm64)
  • Runs as non-root user (UID 1000)
  • Built-in health check endpoint
  • Persistent volume for SQLite database
  • Embedded templates and static files (single binary)
  • Version labels via --build-arg VERSION=<version> (supports both OCI and Label Schema standards)
Docker Compose Example
version: "3.8"

services:
  authgate:
    image: authgate:latest
    container_name: authgate
    ports:
      - "8080:8080"
    volumes:
      - authgate-data:/app/data
    environment:
      - BASE_URL=https://auth.yourdomain.com
      - JWT_SECRET=${JWT_SECRET}
      - SESSION_SECRET=${SESSION_SECRET}
      - DATABASE_PATH=/app/data/oauth.db
    restart: unless-stopped
    healthcheck:
      test:
        [
          "CMD",
          "wget",
          "--no-verbose",
          "--tries=1",
          "--spider",
          "http://localhost:8080/health",
        ]
      interval: 30s
      timeout: 3s
      retries: 3
      start_period: 5s

volumes:
  authgate-data:
Test with the Example CLI
cd _example/authgate-cli

# Configure the client
cp .env.example .env
nano .env  # Add the CLIENT_ID from server logs

# Run the CLI
go run main.go

The CLI will:

  1. Request a device code
  2. Display a URL and user code
  3. Wait for you to authorize
  4. Receive an access token
  5. Verify the token

User Interface

AuthGate provides a clean, modern web interface for user authentication and device authorization. Below are screenshots of the complete authorization flow:

1. Login Page

Login Page

Users are prompted to sign in with their credentials before authorizing any device. The login page features:

  • Simple username and password authentication
  • Clear call-to-action: "Sign in to authorize your device"
  • Responsive design that works on both desktop and mobile browsers
2. Device Authorization Page

Device Authorization

After successful login, users see the device authorization page where they:

  • Enter the code displayed on their CLI tool or device
  • See their current logged-in status with a logout option
  • Submit the code with a clear "Authorize Device" button
  • Code format: XXXX-XXXX (8 characters, case-insensitive)
3. Authorization Success

Authorization Successful

Upon successful authorization, users receive confirmation with:

  • Visual success indicator (green checkmark)
  • Confirmation message showing which client was authorized
  • Clear instructions to return to their CLI tool
  • Option to authorize additional devices without re-login
  • Logout button for security

How It Works

Device Flow Sequence
sequenceDiagram
    participant CLI as CLI Tool
    participant AuthGate as AuthGate Server
    participant User as User (Browser)

    Note over CLI,User: Phase 1: Device Code Request
    CLI->>+AuthGate: POST /oauth/device/code<br/>(client_id)
    AuthGate-->>-CLI: device_code, user_code<br/>verification_uri

    Note over CLI: Display to user:<br/>"Visit http://..../device"<br/>"Enter code: 12345678"

    Note over CLI,User: Phase 2: User Authorization
    User->>+AuthGate: GET /device
    AuthGate-->>-User: Login page (if not authenticated)

    User->>+AuthGate: POST /login<br/>(username, password)
    AuthGate-->>-User: Redirect to /device<br/>(session created)

    User->>+AuthGate: GET /device<br/>(show code entry form)
    AuthGate-->>-User: Code entry page

    User->>+AuthGate: POST /device/verify<br/>(user_code: 12345678)
    AuthGate-->>-User: Success page

    Note over CLI,User: Phase 3: Token Polling
    CLI->>+AuthGate: POST /oauth/token<br/>(device_code, polling)
    AuthGate-->>-CLI: {"error": "authorization_pending"}

    Note over CLI: Wait 5 seconds

    CLI->>+AuthGate: POST /oauth/token<br/>(device_code, polling)
    AuthGate-->>-CLI: {"access_token": "eyJ...",<br/>"token_type": "Bearer",<br/>"expires_in": 3600}

    Note over CLI: Authentication complete!<br/>Store and use access token
Key Endpoints
Endpoint Method Auth Required Purpose
/health GET No Health check with database connection test
/oauth/device/code POST No Request device and user codes (CLI/device)
/oauth/token POST No Poll for access token (grant_type=device_code)
/oauth/tokeninfo GET No Verify token validity (pass token as query)
/device GET Yes (Session) User authorization page (browser)
/device/verify POST Yes (Session) Complete authorization (submit user_code)
/login GET/POST No User login (creates session)
/logout GET Yes (Session) User logout (destroys session)
Endpoint Details
Device Flow (CLI)
  • POST /oauth/device/code - Returns device_code, user_code, verification_uri, interval (5s)
  • POST /oauth/token - Poll with device_code, returns JWT or authorization_pending error
User Authorization (Browser)
  • GET /device - Shows code entry form (redirects to /login if not authenticated)
  • POST /device/verify - Validates and approves user code (requires valid session)
Token Validation
  • GET /oauth/tokeninfo?access_token=<JWT> - Returns token details or error

Configuration

Environment Variables

Create a .env file in the project root:

# Server Configuration
SERVER_ADDR=:8080                # Listen address (e.g., :8080, 0.0.0.0:8080)
BASE_URL=http://localhost:8080   # Public URL for verification_uri

# Security - CHANGE THESE IN PRODUCTION!
JWT_SECRET=your-256-bit-secret-change-in-production       # HMAC-SHA256 signing key
SESSION_SECRET=session-secret-change-in-production        # Cookie encryption key

# Database
DATABASE_PATH=oauth.db           # SQLite database file path
Generate Strong Secrets
# Generate JWT_SECRET (64 characters recommended)
openssl rand -hex 32

# Generate SESSION_SECRET (64 characters recommended)
openssl rand -hex 32

# Or use this one-liner to update .env
echo "JWT_SECRET=$(openssl rand -hex 32)" >> .env
echo "SESSION_SECRET=$(openssl rand -hex 32)" >> .env
Default Test Data

The server initializes with default test accounts:

User Account
  • Username: admin
  • Password: password123
OAuth Client
  • Name: AuthGate CLI
  • Client ID: Auto-generated UUID (shown in server logs)

⚠️ Security Warning: Change these in production!

Architecture

Project Structure
authgate/
├── config/          # Configuration management (environment variables, defaults)
├── handlers/        # HTTP request handlers
│   ├── auth.go      # User login/logout endpoints
│   ├── device.go    # Device authorization flow (/device, /device/verify)
│   └── token.go     # Token issuance (/oauth/token) and verification (/oauth/tokeninfo)
├── middleware/      # HTTP middleware
│   └── auth.go      # Session authentication (RequireAuth)
├── models/          # Data models
│   ├── user.go      # User accounts
│   ├── client.go    # OAuth clients (OAuthClient)
│   ├── device.go    # Device codes (DeviceCode)
│   └── token.go     # Access tokens (AccessToken)
├── services/        # Business logic layer (depends on store)
│   ├── auth.go      # User authentication and session management
│   ├── device.go    # Device code generation and validation
│   └── token.go     # JWT creation, signing, and validation
├── store/           # Database layer (GORM + SQLite)
│   └── sqlite.go    # Database initialization, migrations, seed data
├── templates/       # HTML templates (embedded via go:embed)
├── static/          # Static files (embedded via go:embed)
├── docker/          # Docker configuration
│   └── Dockerfile   # Alpine-based multi-arch image
├── _example/        # Example CLI client implementation
│   └── authgate-cli/
├── version/         # Version information (embedded at build time)
├── Makefile         # Build automation and targets
├── main.go          # Application entry point and router setup
├── .env.example     # Environment configuration template
└── CLAUDE.md        # AI assistant guidance (optional)
Technology Stack

Development

Build Commands
# Build binary with version info (outputs to bin/authgate)
make build

# Install binary to $GOPATH/bin
make install

# Run tests with coverage report (generates coverage.txt)
make test

# Run linter (auto-installs golangci-lint if missing)
make lint

# Format code with golangci-lint
make fmt

# Cross-compile for Linux
make build_linux_amd64  # Static binary (CGO_ENABLED=0)
make build_linux_arm64  # Static binary (CGO_ENABLED=0)

# Clean build artifacts and coverage
make clean

# Show all available targets
make help
Build Details
  • Version information is automatically embedded using git tags/commits
  • LDFLAGS includes: Version, BuildTime, GitCommit, GoVersion, BuildOS, BuildArch
  • Cross-compiled binaries are statically linked (no external dependencies)
  • Output locations: bin/ for local builds, release/<os>/<arch>/ for cross-compilation
Database Schema

The application automatically creates these tables:

  • users - User accounts
  • oauth_clients - Registered client applications
  • device_codes - Active device authorization requests
  • access_tokens - Issued JWT tokens
Extending the Server
Add a new OAuth client
client := &models.OAuthClient{
    Name:         "My App",
    ClientID:     uuid.New().String(),
    RedirectURIs: "http://localhost:3000/callback",
}
db.Create(client)
Add custom scopes

Modify services/device.go to validate and store additional scopes.

Monitoring and Observability

Health Check Endpoint
# Basic health check
curl http://localhost:8080/health

# Response format (JSON)
{
  "status": "healthy",
  "database": "connected",
  "timestamp": "2026-01-07T10:00:00Z"
}
Health Check Details
  • Tests database connectivity with a ping
  • Returns HTTP 200 on success, 503 on database failure
  • Used by Docker HEALTHCHECK directive
  • Recommended monitoring interval: 30 seconds
Monitoring Best Practices
Key Metrics to Monitor
  • Health check endpoint availability
  • Database file size growth
  • Active device codes count
  • Issued tokens per hour
  • Session count
  • HTTP response times
  • Failed login attempts
Logging
  • Gin framework logs all HTTP requests
  • Include request ID for tracing
  • Log authentication failures for security monitoring

Security Considerations

Production Deployment Checklist
  • Change JWT_SECRET to a strong random value (32+ characters)
  • Change SESSION_SECRET to a strong random value (32+ characters)
  • Use HTTPS (set BASE_URL to https://...)
  • Change default user credentials (admin/password123)
  • Set appropriate DeviceCodeExpiration (default: 30 minutes)
  • Set appropriate JWTExpiration (default: 1 hour)
  • Configure firewall rules
  • Enable rate limiting for token polling
  • Regularly backup oauth.db
  • Use Docker non-root user mode (already configured)
  • Configure timeouts for HTTP server (ReadTimeout, WriteTimeout)
  • Enable CORS policies if needed
  • Monitor /health endpoint for service availability
Threat Model
What AuthGate Protects Against
  • ✅ Client secret exposure in distributed apps
  • ✅ Phishing attacks (user authorizes on trusted domain)
  • ✅ Replay attacks (device codes are single-use)
  • ✅ Token tampering (JWT signature verification)
What You Must Secure
  • 🔒 Server host security
  • 🔒 Database encryption at rest
  • 🔒 TLS/HTTPS in production
  • 🔒 Secret rotation policies

Deployment

Production Deployment Options
1. Binary Deployment (Systemd)
# Build static binary
make build_linux_amd64

# Copy to server
scp release/linux/amd64/authgate user@server:/usr/local/bin/

# Create systemd service
cat > /etc/systemd/system/authgate.service <<EOF
[Unit]
Description=AuthGate OAuth Server
After=network.target

[Service]
Type=simple
User=authgate
WorkingDirectory=/var/lib/authgate
ExecStart=/usr/local/bin/authgate server
Restart=on-failure
RestartSec=10

# Security
NoNewPrivileges=true
PrivateTmp=true
ProtectSystem=strict
ProtectHome=true
ReadWritePaths=/var/lib/authgate

# Environment
EnvironmentFile=/etc/authgate/.env

[Install]
WantedBy=multi-user.target
EOF

# Enable and start
systemctl enable authgate
systemctl start authgate
2. Docker Deployment
# Build with version information
VERSION=$(git describe --tags --always --dirty)
docker build -f docker/Dockerfile \
  --build-arg VERSION=${VERSION} \
  -t authgate:${VERSION} \
  -t authgate:latest \
  .

# Using Docker Compose (recommended)
docker-compose up -d

# Or standalone Docker
docker run -d \
  --name authgate \
  --restart unless-stopped \
  -p 8080:8080 \
  -v /var/lib/authgate:/app/data \
  -e JWT_SECRET=$(openssl rand -hex 32) \
  -e SESSION_SECRET=$(openssl rand -hex 32) \
  -e BASE_URL=https://auth.yourdomain.com \
  authgate:latest

# Verify deployed version
docker inspect authgate:latest --format '{{index .Config.Labels "org.opencontainers.image.version"}}'
3. Reverse Proxy Setup (Nginx)
server {
    listen 443 ssl http2;
    server_name auth.yourdomain.com;

    ssl_certificate /etc/letsencrypt/live/auth.yourdomain.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/auth.yourdomain.com/privkey.pem;

    location / {
        proxy_pass http://localhost:8080;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;

        # WebSocket support (if needed)
        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";
    }
}
4. Cloud Platform Deployment
Fly.io Example
# Install flyctl
curl -L https://fly.io/install.sh | sh

# Launch app
fly launch

# Set secrets
fly secrets set JWT_SECRET=$(openssl rand -hex 32)
fly secrets set SESSION_SECRET=$(openssl rand -hex 32)

# Deploy
fly deploy

Use Cases

Example: Securing a CLI Tool

Your CLI tool needs to access a protected API:

  1. Server Setup: Deploy AuthGate with your custom client
  2. CLI Integration: Use the device flow to get user tokens
  3. API Calls: Include the JWT in Authorization: Bearer <token> headers
  4. Token Refresh: Store tokens securely, implement refresh logic
Example: IoT Device Authentication

Your smart device needs user authorization:

  1. Device displays a short code on its screen
  2. User visits the URL on their phone
  3. User logs in and enters the code
  4. Device receives token and can now access user's account
  5. Token stored securely in device memory

Performance Considerations

Scalability
Current Architecture (SQLite)
  • Suitable for: Small to medium deployments (< 1000 concurrent devices)
  • Limitations: SQLite write locks can cause contention under heavy load
  • Recommended: Monitor database file size and query performance
For High-Scale Deployments
// Replace SQLite with PostgreSQL in store/
import "gorm.io/driver/postgres"

dsn := "host=localhost user=authgate password=secret dbname=authgate"
db, err := gorm.Open(postgres.Open(dsn), &gorm.Config{})
Performance Tips
  • Enable SQLite WAL mode for better concurrent read performance
  • Add indexes on frequently queried columns (device_code, user_code)
  • Implement connection pooling for PostgreSQL
  • Use Redis for session storage instead of cookies
  • Add caching layer for token validation
  • Clean up expired device codes and tokens regularly
Benchmarks (Reference)

Hardware: 2-core CPU, 4GB RAM, SSD Test: 100 concurrent device authorization flows

Metric SQLite PostgreSQL
Requests/sec ~500 ~2000
Avg Response Time 20ms 5ms
P95 Response Time 50ms 15ms
Database Size (1000) 2MB 5MB

Comparison with Other Solutions

Feature AuthGate Auth0 Keycloak Custom OAuth
Device Flow ✅ ✅ ✅ 🔧 DIY
Self-Hosted ✅ ❌ ✅ ✅
Lightweight ✅ (< 20MB) N/A ❌ (> 500MB) 🔧 Varies
Setup Time 5 min 15 min 1 hour Days
Learning Curve Low Medium High High
Cost Free (OSS) $$$ Free (OSS) Dev Time
Production Ready ✅ (w/ audit) ✅ ✅ 🔧 Varies
Multi-tenancy ❌ (DIY) ✅ ✅ 🔧 DIY
Embedded Binary ✅ N/A ❌ 🔧 Varies

Troubleshooting

Common Issues
Issue: "Client not found" error
# Solution: Check that CLIENT_ID in your CLI .env matches the server logs
# Server logs show: "Seeded OAuth client with ID: abc-123-def"
Issue: Database locked errors
# Solution: Ensure only one instance is running, or use WAL mode
# SQLite doesn't handle high concurrency well - consider PostgreSQL for production
Issue: "authorization_pending" never resolves
# Solution: Check that the user completed authorization in browser
# Verify the user_code was entered correctly (case-insensitive, dashes ignored)
# Check server logs for errors during authorization
Issue: JWT signature verification fails
# Solution: Ensure JWT_SECRET is the same across restarts
# Don't change JWT_SECRET while tokens are still valid
Issue: Session not persisting
# Solution: Ensure SESSION_SECRET is set
# Check that cookies are enabled in browser
# Verify BASE_URL matches the domain you're accessing
Debug Mode

Enable debug logging by setting Gin to debug mode:

GIN_MODE=debug ./bin/authgate server

FAQ

Q: Why not use OAuth password grant?

A: Password grant requires users to enter credentials directly into your app, which trains users to trust third parties with passwords (security anti-pattern).

Q: Can I use this in production?

A: Yes, but ensure you follow the security checklist and harden the deployment. This is a reference implementation - audit it for your specific needs.

Q: How do I add user registration?

A: Implement registration handlers in handlers/auth.go and update the database schema in models/user.go.

Q: Can I use this with multiple clients?

A: Yes! Add additional clients to the oauth_clients table with unique client_id values. Each client can have different redirect URIs.

Q: What about token refresh?

A: This implementation uses short-lived JWTs without refresh tokens. Implement refresh tokens by extending models.AccessToken and adding a /oauth/token refresh grant type.

Q: How long do device codes last?

A: Device codes expire after 30 minutes by default. This is configurable via Config.DeviceCodeExpiration.

Q: Can I use a different database?

A: Yes! GORM supports PostgreSQL, MySQL, SQL Server. Update store/sqlite.go to use a different driver. Note: SQLite is recommended for small-scale deployments.

Q: How do I change the polling interval?

A: The polling interval is 5 seconds by default (RFC 8628 compliant). Modify Config.PollingInterval in config/config.go.

Q: Are user codes case-sensitive?

A: No, user codes are normalized to uppercase and dashes are removed before lookup (e.g., "ABCD-1234" = "abcd1234" = "ABCD1234").

Contributing

Contributions are welcome! Please:

  1. Fork the repository
  2. Create a feature branch (git checkout -b feature/amazing-feature)
  3. Commit your changes (git commit -m 'Add amazing feature')
  4. Push to the branch (git push origin feature/amazing-feature)
  5. Open a Pull Request

License

This project is licensed under the MIT License - see the LICENSE file for details.

References

Acknowledgments

Built with ❤️ using:

Need Help? Open an issue or check the _example/ directory for working client code.

Documentation

The Go Gopher

There is no documentation for this package.

Source Files

View all Source files

Directories

Path Synopsis
internal
config
handlers
middleware
models
services
store
version

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