Add simple master key provider for secret encryption

services/secrets/masterkey.go

@@ -0,0 +1,27 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package secrets
+
+import (
+	"fmt"
+)
+
+// ErrMasterKeySealed is returned when trying to use master key that is sealed
+var ErrMasterKeySealed = fmt.Errorf("master key sealed")
+
+// MasterKeyProvider provides master key used for encryption
+type MasterKeyProvider interface {
+	Init() error
+
+	GenerateMasterKey() ([][]byte, error)
+
+	Unseal(secret []byte) error
+
+	Seal() error
+
+	IsSealed() bool
+
+	GetMasterKey() ([]byte, error)
+}