---
title: Configuration
description: Configuring a Keysmith engine instance.
---

Keysmith uses the functional options pattern for engine construction.

## Default configuration

```go
type Config struct {
    DefaultPrefix      string          // "sk"
    DefaultEnvironment key.Environment // key.EnvLive
    DefaultKeyLength   int             // 64 (hex characters)
}
```

## Engine options

```go
eng, err := keysmith.NewEngine(
    keysmith.WithStore(store),
    keysmith.WithHasher(customHasher),
    keysmith.WithKeyGenerator(customGen),
    keysmith.WithRateLimiter(limiter),
    keysmith.WithExtension(auditPlugin),
    keysmith.WithLogger(logger),
)
```

| Option | Description |
| ------ | ----------- |
| `WithStore(store.Store)` | **Required.** Sets the composite store backend. |
| `WithHasher(Hasher)` | Custom key hasher. Defaults to SHA-256. |
| `WithKeyGenerator(KeyGenerator)` | Custom key generator. Defaults to `{prefix}_{env}_{64 hex}`. |
| `WithRateLimiter(RateLimiter)` | Pluggable rate limiter for validation. No default. |
| `WithExtension(plugin.Plugin)` | Registers a lifecycle plugin. |
| `WithLogger(*slog.Logger)` | Structured logger. Defaults to `slog.Default()`. |

## Key format

The default key generator produces keys in the format:

```text
{prefix}_{environment}_{64 hex characters}
```

Example: `sk_live_a3f8b2c9e1d4f5a6b7c8d9e0f1a2b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0`

## Pluggable interfaces

### Hasher

```go
type Hasher interface {
    Hash(rawKey string) string
    Verify(rawKey, hash string) bool
}
```

The default uses SHA-256 with constant-time comparison.

### KeyGenerator

```go
type KeyGenerator interface {
    Generate(prefix string, env key.Environment) (string, error)
}
```

### RateLimiter

```go
type RateLimiter interface {
    Allow(ctx context.Context, keyID string, limit int, window time.Duration) (bool, error)
}
```