feat: add VPNsecure.me support (#848)

- `OPENVPN_ENCRYPTED_KEY` environment variable 
- `OPENVPN_ENCRYPTED_KEY_SECRETFILE` environment variable 
- `OPENVPN_KEY_PASSPHRASE` environment variable 
- `OPENVPN_KEY_PASSPHRASE_SECRETFILE` environment variable 
- `PREMIUM_ONLY` environment variable
- OpenVPN user and password not required for vpnsecure provider

internal/openvpn/auth.go

@@ -1,65 +1,56 @@
 package openvpn
 
 import (
-	"io"
+	"fmt"
+	"io/ioutil"
 	"os"
 	"strings"
 )
 
 // WriteAuthFile writes the OpenVPN auth file to disk with the right permissions.
 func (c *Configurator) WriteAuthFile(user, password string) error {
-	file, err := os.Open(c.authFilePath)
-
-	if err != nil && !os.IsNotExist(err) {
-		return err
-	}
-
-	if os.IsNotExist(err) {
-		file, err = os.OpenFile(c.authFilePath, os.O_WRONLY|os.O_CREATE, 0400)
-		if err != nil {
-			return err
-		}
-		_, err = file.WriteString(user + "\n" + password)
-		if err != nil {
-			_ = file.Close()
-			return err
-		}
-		err = file.Chown(c.puid, c.pgid)
-		if err != nil {
-			_ = file.Close()
-			return err
-		}
-		return file.Close()
-	}
-
-	data, err := io.ReadAll(file)
-	if err != nil {
-		_ = file.Close()
-		return err
-	}
-	if err := file.Close(); err != nil {
-		return err
-	}
-
-	lines := strings.Split(string(data), "\n")
-	if len(lines) > 1 && lines[0] == user && lines[1] == password {
-		return nil
-	}
-
-	c.logger.Info("username and password changed in " + c.authFilePath)
-	file, err = os.OpenFile(c.authFilePath, os.O_TRUNC|os.O_WRONLY, 0400)
-	if err != nil {
-		return err
-	}
-	_, err = file.WriteString(user + "\n" + password)
-	if err != nil {
-		_ = file.Close()
-		return err
-	}
-	err = file.Chown(c.puid, c.pgid)
-	if err != nil {
-		_ = file.Close()
-		return err
-	}
-	return file.Close()
+	content := strings.Join([]string{user, password}, "\n")
+	return writeIfDifferent(c.authFilePath, content, c.puid, c.pgid)
+}
+
+// WriteAskPassFile writes the OpenVPN askpass file to disk with the right permissions.
+func (c *Configurator) WriteAskPassFile(passphrase string) error {
+	return writeIfDifferent(c.askPassPath, passphrase, c.puid, c.pgid)
+}
+
+func writeIfDifferent(path, content string, puid, pgid int) (err error) {
+	fileStat, err := os.Stat(path)
+	if err != nil && !os.IsNotExist(err) {
+		return fmt.Errorf("obtaining file information: %w", err)
+	}
+
+	const perm = os.FileMode(0400)
+	var writeData, setChown bool
+	if os.IsNotExist(err) {
+		writeData = true
+		setChown = true
+	} else {
+		data, err := os.ReadFile(path)
+		if err != nil {
+			return fmt.Errorf("reading file: %w", err)
+		}
+		writeData = string(data) != content
+		setChown = fileStat.Mode().Perm() != perm
+	}
+
+	if writeData {
+		err = ioutil.WriteFile(path, []byte(content), perm)
+		if err != nil {
+			return fmt.Errorf("writing file: %w", err)
+		}
+	}
+
+	if setChown {
+		err = os.Chown(path, puid, pgid)
+		if err != nil {
+			return fmt.Errorf("setting file permissions: %w", err)
+		}
+	}
+
+	return nil
 }