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README.md

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+# Forward Auth TOTP
+
+A lightweight forward authentication service for Caddy (or any reverse proxy) that uses TOTP (Time-based One-Time Password) tokens for user authentication.
+
+## Features
+
+- 🔐 TOTP-based authentication (compatible with Google Authenticator, Authy, 1Password, etc.)
+- 🎫 JWT session management with configurable duration
+- 👥 Support for multiple users (1-20+ TOTP seeds)
+- 🪶 Lightweight SQLite database
+- 🚀 Single binary deployment
+- 🔄 Works with Caddy's `forward_auth` directive
+- 📱 Mobile-friendly login page
+
+## Prerequisites
+
+- Go 1.21 or higher
+- SQLite3
+- Caddy v2 (or any reverse proxy that supports forward authentication)
+
+## Installation
+
+### Clone the repository
+```bash
+git clone https://github.com/yourusername/forward-auth-totp.git
+cd forward-auth-totp
+```
+
+### Install dependencies
+```bash
+go mod download
+```
+
+### Build the application
+```bash
+go build -o forward-auth main.go
+```
+
+## Configuration
+
+### Environment Variables
+
+| Variable | Description | Default | Required |
+|----------|-------------|---------|----------|
+| `JWT_SECRET` | Secret key for signing JWT tokens | (insecure default) | **Recommended** |
+
+**Important:** Always set a secure `JWT_SECRET` in production:
+```bash
+export JWT_SECRET="your-very-secure-random-secret-here-min-32-chars"
+```
+
+Generate a secure secret:
+```bash
+openssl rand -base64 32
+```
+
+### Application Constants
+
+You can modify these constants in `main.go`:
+
+- `sessionDuration`: JWT session duration (default: 24 hours)
+- `dbFile`: SQLite database file path (default: `auth.db`)
+- `jwtCookie`: Cookie name for JWT token (default: `auth_token`)
+
+## Usage
+
+### First Run
+
+On first run, the application will automatically generate a TOTP seed:
+```bash
+./forward-auth
+```
+
+Output:
+```
+No seeds found, generating one...
+New TOTP seed generated:
+Secret: JBSWY3DPEHPK3PXP
+OTPAuth URL: otpauth://totp/ForwardAuthApp:user?secret=JBSWY3DPEHPK3PXP&issuer=ForwardAuthApp
+Use this to set up your authenticator app.
+Starting auth server on :3000
+```
+
+Scan the QR code (use the OTPAuth URL with a QR generator) or manually enter the secret into your authenticator app.
+
+### Generate Additional TOTP Seeds
+
+For multiple users, generate additional seeds:
+```bash
+./forward-auth -generate
+```
+
+Each seed can be used by a different user with their own authenticator app.
+
+### Running as a Service
+
+#### systemd (Linux)
+
+Create `/etc/systemd/system/forward-auth.service`:
+```ini
+[Unit]
+Description=Forward Auth TOTP Service
+After=network.target
+
+[Service]
+Type=simple
+User=www-data
+WorkingDirectory=/opt/forward-auth
+Environment="JWT_SECRET=your-secure-secret-here"
+ExecStart=/opt/forward-auth/forward-auth
+Restart=on-failure
+RestartSec=5s
+
+[Install]
+WantedBy=multi-user.target
+```
+
+Enable and start:
+```bash
+sudo systemctl enable forward-auth
+sudo systemctl start forward-auth
+```
+
+## Caddy Configuration
+
+### Basic Configuration
+```caddyfile
+# Your protected application
+app.example.com {
+    forward_auth localhost:3000 {
+        uri /verify
+        copy_headers X-Original-URI
+    }
+    
+    reverse_proxy localhost:8080
+}
+
+# Auth service (optional, if you want it accessible externally)
+auth.example.com {
+    reverse_proxy localhost:3000
+}
+```
+
+### Advanced Configuration with Error Handling
+```caddyfile
+app.example.com {
+    # Allow access to login page without auth
+    @login {
+        path /login*
+    }
+    handle @login {
+        reverse_proxy localhost:3000
+    }
+    
+    # Protect everything else
+    forward_auth localhost:3000 {
+        uri /verify
+        copy_headers X-Original-URI
+    }
+    
+    reverse_proxy localhost:8080
+}
+```
+
+### Multiple Protected Services
+```caddyfile
+# Auth service
+auth.example.com {
+    reverse_proxy localhost:3000
+}
+
+# Protected app 1
+app1.example.com {
+    forward_auth auth.example.com {
+        uri /verify
+        copy_headers X-Original-URI
+    }
+    reverse_proxy localhost:8080
+}
+
+# Protected app 2
+app2.example.com {
+    forward_auth auth.example.com {
+        uri /verify
+        copy_headers X-Original-URI
+    }
+    reverse_proxy localhost:8081
+}
+```
+
+## API Endpoints
+
+| Endpoint | Method | Description |
+|----------|--------|-------------|
+| `/verify` | GET | Verify JWT token (for forward auth) |
+| `/login` | GET | Display login form |
+| `/login` | POST | Process OTP submission |
+| `/health` | GET | Health check endpoint |
+
+## Security Considerations
+
+### Production Checklist
+
+- [ ] Set a strong `JWT_SECRET` environment variable
+- [ ] Enable HTTPS and uncomment `Secure: true` in cookie settings
+- [ ] Restrict database file permissions: `chmod 600 auth.db`
+- [ ] Run the service as a non-root user
+- [ ] Keep the TOTP secrets secure and backed up
+- [ ] Consider rate limiting on the `/login` endpoint
+- [ ] Monitor failed authentication attempts
+
+### HTTPS Configuration
+
+For production, uncomment the `Secure` flag in `main.go`:
+```go
+http.SetCookie(w, &http.Cookie{
+    Name:     jwtCookie,
+    Value:    tokenStr,
+    Expires:  time.Now().Add(sessionDuration),
+    HttpOnly: true,
+    SameSite: http.SameSiteLaxMode,
+    Secure:   true, // Uncomment this line
+    Path:     "/",
+})
+```
+
+## Database Management
+
+### Backup
+```bash
+cp auth.db auth.db.backup
+```
+
+### View All Seeds
+```bash
+sqlite3 auth.db "SELECT * FROM seeds;"
+```
+
+### Remove a Seed
+```bash
+sqlite3 auth.db "DELETE FROM seeds WHERE id = 1;"
+```
+
+### Reset Database
+```bash
+rm auth.db
+./forward-auth  # Will generate a new seed automatically
+```
+
+## Troubleshooting
+
+### "Invalid OTP" Error
+
+- Ensure your device time is synchronized (TOTP is time-based)
+- Check that you're using the correct seed in your authenticator app
+- Verify the OTP code hasn't expired (codes are valid for 30 seconds)
+
+### Authentication Not Working
+
+- Check Caddy logs: `journalctl -u caddy -f`
+- Check forward-auth logs: `journalctl -u forward-auth -f`
+- Verify the forward auth service is running: `curl http://localhost:3000/health`
+- Ensure `X-Original-URI` header is being passed correctly
+
+### Cookie Not Persisting
+
+- Verify you're using HTTPS in production with `Secure: true`
+- Check that the cookie path matches your application structure
+- Ensure `SameSite` attribute is compatible with your setup
+
+## Performance
+
+This application is designed for light usage (1-20 users, <100 requests/day):
+
+- **Memory footprint:** ~10-15 MB
+- **CPU usage:** Minimal (<1% on modern systems)
+- **Database size:** <1 KB for up to 20 seeds
+- **Startup time:** <100ms
+
+## Development
+
+### Run in Development Mode
+```bash
+go run main.go
+```
+
+### Run Tests
+```bash
+go test -v ./...
+```
+
+### Build for Different Platforms
+```bash
+# Linux
+GOOS=linux GOARCH=amd64 go build -o forward-auth-linux main.go
+
+# macOS
+GOOS=darwin GOARCH=amd64 go build -o forward-auth-macos main.go
+
+# Windows
+GOOS=windows GOARCH=amd64 go build -o forward-auth.exe main.go
+```
+
+## Contributing
+
+Contributions are welcome! Please feel free to submit a Pull Request.
+
+## License
+
+MIT License - see LICENSE file for details
+
+## Acknowledgments
+
+- [golang-jwt/jwt](https://github.com/golang-jwt/jwt) - JWT implementation
+- [pquerna/otp](https://github.com/pquerna/otp) - TOTP implementation
+- [mattn/go-sqlite3](https://github.com/mattn/go-sqlite3) - SQLite driver
+
+## Support
+
+For issues and questions, please open an issue on GitHub.
+
+---
+
+**Note:** This is a simple authentication service suitable for personal or small team use. For larger deployments, consider more robust authentication solutions with features like account lockout, audit logging, and multi-factor authentication options.