public override async Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
        {
            string clientId;
            string clientSecret;

            if (!context.TryGetBasicCredentials(out clientId, out clientSecret))
            {
                return;
            }
            //如果用户未申请refreshtoken  不进行验证
            var client = await _clientApp.Get(clientId);

            if (client == null)
            {
                return;
            }
            if (client.Secret != clientSecret)
            {
                return;
            }

            context.OwinContext.Set <string>("as:client_id", clientId);
            context.OwinContext.Set <string>("as:clientRefreshTokenLifeTime", client.RefreshTokenLifeTime.ToString());

            context.Validated(clientId);


            await base.ValidateClientAuthentication(context);
        }