feat: add version flag using build metadata

- Add a version command-line flag that prints the build version and exits
- Use Go build metadata to report the application version, with a fallback when unavailable

Signed-off-by: appleboy <appleboy.tw@gmail.com>

Author: appleboy

config.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"runtime/debug"
 	"strconv"
 	"strings"
 	"time"
@@ -37,6 +38,7 @@ var (
 	flagScope        *string
 	flagTokenFile    *string
 	flagDevice       *bool
+	flagVersion      *bool
 )
 
 const (
@@ -82,6 +84,7 @@ func init() {
 		false,
 		"Force Device Code Flow (skip browser detection)",
 	)
+	flagVersion = flag.Bool("version", false, "Print version and exit")
 }
 
 func initConfig() {
@@ -92,6 +95,16 @@ func initConfig() {
 
 	flag.Parse()
 
+	// --version prints build version and exits immediately.
+	if *flagVersion {
+		if build, ok := debug.ReadBuildInfo(); ok {
+			fmt.Println(build.Main.Version)
+		} else {
+			fmt.Println("unknown version")
+		}
+		os.Exit(0)
+	}
+
 	// --device forces Device Code Flow unconditionally.
 	forceDevice = *flagDevice