feat: encrypt private keys saved on disk and in database (#682)

Co-authored-by: Kyle Mendell <kmendell@ofkm.us>

backend/internal/utils/jwk/key_provider_database.go

@@ -0,0 +1,109 @@
+package jwk
+
+import (
+	"context"
+	"encoding/base64"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/lestrrat-go/jwx/v3/jwk"
+	"gorm.io/gorm"
+
+	"github.com/pocket-id/pocket-id/backend/internal/model"
+	cryptoutils "github.com/pocket-id/pocket-id/backend/internal/utils/crypto"
+)
+
+const PrivateKeyDBKey = "jwt_private_key.json"
+
+type KeyProviderDatabase struct {
+	db  *gorm.DB
+	kek []byte
+}
+
+func (f *KeyProviderDatabase) Init(opts KeyProviderOpts) error {
+	if len(opts.Kek) == 0 {
+		return errors.New("an encryption key is required when using the 'database' key provider")
+	}
+
+	f.db = opts.DB
+	f.kek = opts.Kek
+
+	return nil
+}
+
+func (f *KeyProviderDatabase) LoadKey() (key jwk.Key, err error) {
+	row := model.KV{
+		Key: PrivateKeyDBKey,
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+	err = f.db.WithContext(ctx).First(&row).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		// Key not present in the database - return nil so a new one can be generated
+		return nil, nil
+	} else if err != nil {
+		return nil, fmt.Errorf("failed to retrieve private key from the database: %w", err)
+	}
+
+	if row.Value == nil || *row.Value == "" {
+		// Key not present in the database - return nil so a new one can be generated
+		return nil, nil
+	}
+
+	// Decode from base64
+	enc, err := base64.StdEncoding.DecodeString(*row.Value)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read encrypted private key: not a valid base64-encoded value: %w", err)
+	}
+
+	// Decrypt the data
+	data, err := cryptoutils.Decrypt(f.kek, enc, nil)
+	if err != nil {
+		return nil, fmt.Errorf("failed to decrypt private key: %w", err)
+	}
+
+	// Parse the key
+	key, err = jwk.ParseKey(data)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse encrypted private key: %w", err)
+	}
+
+	return key, nil
+}
+
+func (f *KeyProviderDatabase) SaveKey(key jwk.Key) error {
+	// Encode the key to JSON
+	data, err := EncodeJWKBytes(key)
+	if err != nil {
+		return fmt.Errorf("failed to encode key to JSON: %w", err)
+	}
+
+	// Encrypt the key then encode to Base64
+	enc, err := cryptoutils.Encrypt(f.kek, data, nil)
+	if err != nil {
+		return fmt.Errorf("failed to encrypt key: %w", err)
+	}
+	encB64 := base64.StdEncoding.EncodeToString(enc)
+
+	// Save to database
+	row := model.KV{
+		Key:   PrivateKeyDBKey,
+		Value: &encB64,
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+	err = f.db.WithContext(ctx).Create(&row).Error
+	if err != nil {
+		// There's one scenario where if Pocket ID is started fresh with more than 1 replica, they both could be trying to create the private key in the database at the same time
+		// In this case, only one of the replicas will succeed; the other one(s) will return an error here, which will cascade down and cause the replica(s) to crash and be restarted (at that point they'll load the then-existing key from the database)
+		return fmt.Errorf("failed to store private key in database: %w", err)
+	}
+
+	return nil
+}
+
+// Compile-time interface check
+var _ KeyProvider = (*KeyProviderDatabase)(nil)