Implement VaultProvider with Transit engine:
- AppRole, Kubernetes, and Token authentication
- Encrypt/Decrypt via /transit/encrypt and /transit/decrypt
- Key lifecycle via /transit/keys API
- Health check via /sys/health
Implement AWSProvider with SDK v2:
- Per-region key naming with alias prefix
- Encrypt/Decrypt via KMS SDK
- Key lifecycle (CreateKey, Disable, ScheduleDeletion, Enable)
- AWS endpoint support for LocalStack testing
Add KMSProvider interface for external key management systems:
- Encrypt/Decrypt operations for DEK wrapping
- Key lifecycle management (Create, Disable, ScheduleDeletion, Enable)
- HealthCheck and Close methods
Implement MemoryProvider for development/testing:
- XOR encryption with HMAC-SHA256 authentication
- Secure random key generation using crypto/rand
- MAC verification to detect wrong keys
Implement DEKCache per ADR-012:
- 15-minute TTL with configurable grace window (1 hour)
- LRU eviction with 1000 entry limit
- Cache key includes (tenantID, artifactID, kmsKeyID) for isolation
- Thread-safe operations with RWMutex
- Secure memory wiping on eviction/cleanup
Add config package with types:
- ProviderType enum (vault, aws, memory)
- VaultConfig with AppRole/Kubernetes/Token auth
- AWSConfig with region and alias prefix
- CacheConfig with TTL, MaxEntries, GraceWindow
- Validation methods for all config types
