feat(security): implement keystore for user authentication keys

* Add ConfigKeyStore for in-memory key management
* Introduce DatabaseKeyStore for PostgreSQL-backed key storage
* Create KeyStoreAuthenticator for API key validation
* Define SQL procedures for key management in PostgreSQL
* Document keystore functionality and usage in KEYSTORE.md

pkg/security/keystore_sql_names.go

@@ -0,0 +1,61 @@
+package security
+
+import "fmt"
+
+// KeyStoreSQLNames holds the configurable stored procedure names used by DatabaseKeyStore.
+// Use DefaultKeyStoreSQLNames() for defaults and MergeKeyStoreSQLNames() for partial overrides.
+type KeyStoreSQLNames struct {
+	GetUserKeys string // default: "resolvespec_keystore_get_user_keys"
+	CreateKey   string // default: "resolvespec_keystore_create_key"
+	DeleteKey   string // default: "resolvespec_keystore_delete_key"
+	ValidateKey string // default: "resolvespec_keystore_validate_key"
+}
+
+// DefaultKeyStoreSQLNames returns a KeyStoreSQLNames with all default resolvespec_keystore_* values.
+func DefaultKeyStoreSQLNames() *KeyStoreSQLNames {
+	return &KeyStoreSQLNames{
+		GetUserKeys: "resolvespec_keystore_get_user_keys",
+		CreateKey:   "resolvespec_keystore_create_key",
+		DeleteKey:   "resolvespec_keystore_delete_key",
+		ValidateKey: "resolvespec_keystore_validate_key",
+	}
+}
+
+// MergeKeyStoreSQLNames returns a copy of base with any non-empty fields from override applied.
+// If override is nil, a copy of base is returned.
+func MergeKeyStoreSQLNames(base, override *KeyStoreSQLNames) *KeyStoreSQLNames {
+	if override == nil {
+		copied := *base
+		return &copied
+	}
+	merged := *base
+	if override.GetUserKeys != "" {
+		merged.GetUserKeys = override.GetUserKeys
+	}
+	if override.CreateKey != "" {
+		merged.CreateKey = override.CreateKey
+	}
+	if override.DeleteKey != "" {
+		merged.DeleteKey = override.DeleteKey
+	}
+	if override.ValidateKey != "" {
+		merged.ValidateKey = override.ValidateKey
+	}
+	return &merged
+}
+
+// ValidateKeyStoreSQLNames checks that all non-empty procedure names are valid SQL identifiers.
+func ValidateKeyStoreSQLNames(names *KeyStoreSQLNames) error {
+	fields := map[string]string{
+		"GetUserKeys": names.GetUserKeys,
+		"CreateKey":   names.CreateKey,
+		"DeleteKey":   names.DeleteKey,
+		"ValidateKey": names.ValidateKey,
+	}
+	for field, val := range fields {
+		if val != "" && !validSQLIdentifier.MatchString(val) {
+			return fmt.Errorf("KeyStoreSQLNames.%s contains invalid characters: %q", field, val)
+		}
+	}
+	return nil
+}