slog: use the slog.LevelVar unmarshal to parse log level flag

cmd/hvpn-node/hvpn-node.go

@@ -102,18 +102,13 @@ func createCliApp() *cli.App {
         Value: "INFO",
         EnvVars: []string{"LOG_LEVEL"},
         Action: func(ctx *cli.Context, s string) error {
-            switch s {
-            case "INFO":
-                slog.SetLogLoggerLevel(slog.LevelInfo)
-            case "DEBUG":
-                slog.SetLogLoggerLevel(slog.LevelDebug)
-            case "WARN":
-                slog.SetLogLoggerLevel(slog.LevelWarn)
-            case "ERROR":
-                slog.SetLogLoggerLevel(slog.LevelError)
-            default:
-                return cli.Exit(fmt.Sprintf("Undefined log level: %s", s), 1)
+            lvl := new(slog.LevelVar)
+            err := lvl.UnmarshalText([]byte(s))
+            if err != nil {
+                slog.Debug("Error on unmarshal log level flag")
+                return err
             }
+            slog.SetLogLoggerLevel(lvl.Level())
             return nil 
         },
     }