给toke一个缓存，防止多次访问

Redis 缓存一个toke 代码如下：

 public static string GetToken()
        {
            RedisClient redisClient = new RedisClient();
            // 先从缓存获取
            string toke = redisClient.Get<string>("toke");
            if (toke != null)
            {
                return toke;
            }
            //缓存中没有找到从外网获取 
            HttpClient httpClient = new HttpClient();
            string reuslt = httpClient.GetAsync("https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid=wx06d6f658f31d964d&secret=8abb7a5ec4cf3f1af0a6dcb1cdd77678").Result.Content.ReadAsStringAsync().Result;
            AccessTokenToolsDTO accessTokenToolsDTO = JsonConvert.DeserializeObject<AccessTokenToolsDTO>(reuslt);
            // 吧toke写入缓存
            redisClient.Set<string>("toke", accessTokenToolsDTO.access_token,TimeSpan.FromSeconds(accessTokenToolsDTO.expires_in-160));
            return accessTokenToolsDTO.access_token;
        }