Add TLS self sign generate command

cmd/sing-box/cmd_generate_vapid.go

@@ -0,0 +1,40 @@
+//go:build go1.20
+
+package main
+
+import (
+	"crypto/ecdh"
+	"crypto/rand"
+	"encoding/base64"
+	"os"
+
+	"github.com/sagernet/sing-box/log"
+
+	"github.com/spf13/cobra"
+)
+
+var commandGenerateVAPIDKeyPair = &cobra.Command{
+	Use:   "vapid-keypair",
+	Short: "Generate VAPID key pair",
+	Run: func(cmd *cobra.Command, args []string) {
+		err := generateVAPIDKeyPair()
+		if err != nil {
+			log.Fatal(err)
+		}
+	},
+}
+
+func init() {
+	commandGenerate.AddCommand(commandGenerateVAPIDKeyPair)
+}
+
+func generateVAPIDKeyPair() error {
+	privateKey, err := ecdh.P256().GenerateKey(rand.Reader)
+	if err != nil {
+		return err
+	}
+	publicKey := privateKey.PublicKey()
+	os.Stdout.WriteString("PrivateKey: " + base64.RawURLEncoding.EncodeToString(privateKey.Bytes()) + "\n")
+	os.Stdout.WriteString("PublicKey: " + base64.RawURLEncoding.EncodeToString(publicKey.Bytes()) + "\n")
+	return nil
+}