chore: OpenVPN user and password as nullable

- Username and password can be the empty string for custom provider

internal/provider/custom/openvpnconf.go

@@ -74,7 +74,7 @@ func modifyConfig(lines []string, connection models.Connection,
 	modified = append(modified, "pull-filter ignore \"auth-token\"") // prevent auth failed loop
 	modified = append(modified, "auth-retry nointeract")
 	modified = append(modified, "suppress-timestamps")
-	if settings.User != "" {
+	if *settings.User != "" {
 		modified = append(modified, "auth-user-pass "+openvpn.AuthConf)
 	}
 	modified = append(modified, "verb "+strconv.Itoa(*settings.Verbosity))

internal/provider/custom/openvpnconf_test.go

@@ -36,7 +36,7 @@ func Test_modifyConfig(t *testing.T) {
 				"auth bla",
 			},
 			settings: settings.OpenVPN{
-				User:        "user",
+				User:        stringPtr("user"),
 				Ciphers:     []string{"cipher"},
 				Auth:        stringPtr("auth"),
 				MSSFix:      uint16Ptr(1000),