[ApiController]
  [Route("api/[controller]")]
  public class Auth3Controller : ControllerBase
  {

    private readonly string _agentId = "1000002";
    private readonly string _secret = "Y3f8ESBIBJoC8M_FPHOlpvmghS_Nn2ceFePRVZjw9_E";
    private readonly string _corpId = "wwbf72a7a059eac0f8";
    /// <summary>
    /// 授權地址
    /// </summary>
    private readonly string _auth3url = "https://open.weixin.qq.com/connect/oauth3/authorize";
    /// <summary>
    /// 授權回調地址
    /// </summary>
    private readonly string _callbackurl = "http://******.zicp.vip/auth3callback/api/Auth3/Callback";
    /// <summary>
    /// 獲取access_token地址
    /// </summary>
    private readonly string _gettokenurl = "https://qyapi.weixin.qq.com/cgi-bin/gettoken";
    /// <summary>
    /// 獲取訪問用戶身份地址
    /// </summary>
    private readonly string _getuserurl = "https://qyapi.weixin.qq.com/cgi-bin/user/getuserinfo";


    private readonly ILogger<Auth3Controller> _logger;
    private readonly IHttpClientFactory _clientFactory;
    private readonly IMemoryCache _memoryCache;

    public Auth3Controller(ILogger<Auth3Controller> logger, IHttpClientFactory clientFactory, IMemoryCache memoryCache)
    {
      _logger = logger;
      _clientFactory = clientFactory;
      _memoryCache = memoryCache;
    }   

    [HttpGet]
    public IActionResult Auth3(string redirecturi)
    {
      string strurl = $"{_auth3url}?" +
          $"&appid={_corpId}" +
          $"&redirect_uri={System.Web.HttpUtility.UrlEncode(_callbackurl)}" +
          $"&response_type=code" +
          $"&scope={_secret}" +
          $"&agentid={_agentId}" +
          $"&state={System.Web.HttpUtility.UrlEncode(redirecturi)}#wechat_redirect";
      return Redirect(strurl);
    }

    [HttpGet("Callback")]
    public async Task<IActionResult> Callback(string code, string state)
    {
      /**
       1）code只能消費一次，不能重復消費。比如說，是否存在多個服務器同時消費同一code情況。
       2）code需要在有效期間消費（5分鐘），過期會自動失效。
       */      
      string access_token = await GetAccessToken();
      string url = $"{_getuserurl}?access_token={access_token}&code=[code]";
      HttpResponseMessage response = await _clientFactory.CreateClient().GetAsync(url);
      if (response.StatusCode == System.Net.HttpStatusCode.OK)
      {
        using (var responseStream = await response.Content.ReadAsStreamAsync())
        {
          var userinfo = JsonConvert.DeserializeObject<dynamic>(new StreamReader(responseStream).ReadToEnd());
          int errcode = userinfo.errcode;
          if (errcode == 0)
          {
            //企業成員
            string UserId = userinfo.UserId;
            //外部成員
            string OpenId = userinfo.OpenId;
            /**
             userid是系統生成的可以修改一次;
             所以后面的業務邏輯如果遇到錯誤就要重新授權一下;   
             */
            if (UserId==null)
            {
              _memoryCache.Set<string>("UserId", OpenId);
            }
            else
            {
              _memoryCache.Set<string>("UserId", UserId);
            }
          }
          else
          {
            _logger.LogError($"getuserinfo請求錯誤:{userinfo.errmsg}");
            return Ok();
          }
        }
      }      
      return Redirect($"{System.Web.HttpUtility.UrlDecode(state)}?UserId={_memoryCache.Get<string>("UserId")}");
    }
    public async Task<string> GetAccessToken()
    {
      if (_memoryCache.Get<string>("AccessToken") == null)
      {
        string url = $"{_gettokenurl}?corpid={_corpId}&corpsecret={_secret}";
        HttpResponseMessage response = await _clientFactory.CreateClient().GetAsync(url);
        if (response.StatusCode == System.Net.HttpStatusCode.OK)
        {
          using (var responseStream = await response.Content.ReadAsStreamAsync())
          {
            var access_token_result = JsonConvert.DeserializeObject<dynamic>(new StreamReader(responseStream).ReadToEnd());
            int errcode = access_token_result.errcode;
            if (errcode == 0)
            {
              string access_token = access_token_result.access_token;
              int expires_in = access_token_result.expires_in;
              _memoryCache.Set<string>("AccessToken", access_token, DateTimeOffset.Now.AddSeconds(expires_in - 10));
            }
            else
            {
              _logger.LogError($"access_token請求錯誤:{access_token_result.errmsg }");
            }
          }

        }
      }
      return _memoryCache.Get<string>("AccessToken");
    }
  }