Check permissions

clients/permissions/permissions_windows.go

@@ -0,0 +1,38 @@
+//go:build windows
+
+package permissions
+
+import (
+	"fmt"
+
+	"golang.org/x/sys/windows"
+)
+
+// CheckNativeInterfacePermissions checks if the process has sufficient
+// permissions to create a native TUN interface on Windows.
+// This requires Administrator privileges.
+func CheckNativeInterfacePermissions() error {
+	var sid *windows.SID
+	err := windows.AllocateAndInitializeSid(
+		&windows.SECURITY_NT_AUTHORITY,
+		2,
+		windows.SECURITY_BUILTIN_DOMAIN_RID,
+		windows.DOMAIN_ALIAS_RID_ADMINS,
+		0, 0, 0, 0, 0, 0,
+		&sid)
+	if err != nil {
+		return fmt.Errorf("failed to initialize SID: %v", err)
+	}
+	defer windows.FreeSid(sid)
+
+	token := windows.Token(0)
+	member, err := token.IsMember(sid)
+	if err != nil {
+		return fmt.Errorf("failed to check admin group membership: %v", err)
+	}
+
+	if !member {
+		return fmt.Errorf("insufficient permissions: need Administrator to create TUN interface on Windows")
+	}
+	return nil
+}