如何在Flutter上包装验证消息？

dependencies:
  http: ^0.13.4
  crypto: ^3.0.1

import 'package:http/http.dart' as http;
import 'package:crypto/crypto.dart';

String wrapVerificationMessage(String message) {
  // 生成随机的密钥
  var key = 'your_secret_key';
  
  // 计算消息的哈希值
  var bytes = utf8.encode(message);
  var digest = sha256.convert(bytes);
  
  // 使用密钥对哈希值进行加密
  var hmac = Hmac(sha256, utf8.encode(key));
  var signature = hmac.convert(digest.bytes);
  
  // 将消息和签名组合成包装后的验证消息
  var wrappedMessage = '$message|$signature';
  
  return wrappedMessage;
}

void sendVerificationMessage(String message) async {
  var wrappedMessage = wrapVerificationMessage(message);
  
  var url = 'https://example.com/verify';
  
  var response = await http.post(Uri.parse(url), body: {'message': wrappedMessage});
  
  if (response.statusCode == 200) {
    // 处理响应
  } else {
    // 处理错误
  }
}