add unixcrypt build tag

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

internal/dataprovider/unixcrypt.go

@@ -0,0 +1,39 @@
+// Copyright (C) 2019-2023 Nicola Murino
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published
+// by the Free Software Foundation, version 3.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+//go:build unixcrypt
+// +build unixcrypt
+
+package dataprovider
+
+import (
+	"strings"
+
+	"github.com/amoghe/go-crypt"
+
+	"github.com/drakkan/sftpgo/v2/internal/version"
+)
+
+func init() {
+	version.AddFeature("+unixcrypt")
+}
+
+func compareYescryptPassword(hashedPwd, plainPwd string) (bool, error) {
+	lastIdx := strings.LastIndex(hashedPwd, "$")
+	pwd, err := crypt.Crypt(plainPwd, hashedPwd[:lastIdx+1])
+	if err != nil {
+		return false, err
+	}
+	return pwd == hashedPwd, nil
+}