Custom UID and GID for subprocesses and files written (#116) Fix #116

- Environment variables `UID` and `GID`, both defaulting to `1000`
- All subprocesses (openvpn, tinyproxy, etc.) run using the UID and GID given
- All files are written with an ownership for the UID and GID given
- Port forwarded file has also ownership for UID, GID and read permission only

internal/alpine/alpine.go

@@ -0,0 +1,28 @@
+package alpine
+
+import (
+	"os/user"
+
+	"github.com/qdm12/golibs/files"
+	"github.com/qdm12/golibs/logging"
+)
+
+const logPrefix = "alpine configurator"
+
+type Configurator interface {
+	CreateUser(username string, uid int) error
+}
+
+type configurator struct {
+	fileManager files.FileManager
+	lookupUID   func(uid string) (*user.User, error)
+	lookupUser  func(username string) (*user.User, error)
+}
+
+func NewConfigurator(logger logging.Logger, fileManager files.FileManager) Configurator {
+	return &configurator{
+		fileManager: fileManager,
+		lookupUID:   user.LookupId,
+		lookupUser:  user.Lookup,
+	}
+}