set default locale of managed login undefined

Author: tmokmss

webapp/src/app/sign-in/page.tsx

@@ -16,7 +16,9 @@ export default function SignInPage() {
             </p>
 
             <Link
-              href="/api/auth/sign-in?lang=ja"
+              href="/api/auth/sign-in"
+              // you can add a query string to change the locale of cognito managed login page.
+              // href="/api/auth/sign-in?lang=ja"
               className="w-full flex justify-center py-3 px-4 border border-transparent rounded-md shadow-sm text-sm font-medium text-white bg-indigo-600 hover:bg-indigo-700 focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-indigo-500"
               prefetch={false} // prevent CORS error
             >