public async Task Expired_RefreshToken()
        {
            var refreshToken = new RefreshToken
            {
                AccessToken = new Token("access_token") { Client = new Client() { ClientId = "roclient" } },
                LifeTime = 10,
                CreationTime = DateTimeOffset.UtcNow.AddSeconds(-15)
            };
            var handle = Guid.NewGuid().ToString();

            var store = new InMemoryRefreshTokenStore();
            await store.StoreAsync(handle, refreshToken);

            var client = await _clients.FindClientByIdAsync("roclient");

            var validator = Factory.CreateTokenRequestValidator(
                refreshTokens: store);

            var parameters = new NameValueCollection();
            parameters.Add(OidcConstants.TokenRequest.GrantType, "refresh_token");
            parameters.Add(OidcConstants.TokenRequest.RefreshToken, handle);

            var result = await validator.ValidateRequestAsync(parameters, client);

            result.IsError.Should().BeTrue();
            result.Error.Should().Be(OidcConstants.TokenErrors.InvalidGrant);
        }
        public async Task Client_has_no_OfflineAccess_Scope_anymore_at_RefreshToken_Request()
        {
            var refreshToken = new RefreshToken
            {
                AccessToken = new Token("access_token")
                {
                    Client = new Client
                    {
                        ClientId = "roclient_restricted"
                    },
                },
                LifeTime = 600,
                CreationTime = DateTimeOffset.UtcNow
            };
            var handle = Guid.NewGuid().ToString();

            var store = new InMemoryRefreshTokenStore();
            await store.StoreAsync(handle, refreshToken);

            var client = await _clients.FindClientByIdAsync("roclient_restricted");

            var validator = Factory.CreateTokenRequestValidator(
                refreshTokens: store);

            var parameters = new NameValueCollection();
            parameters.Add(Constants.TokenRequest.GrantType, "refresh_token");
            parameters.Add(Constants.TokenRequest.RefreshToken, handle);

            var result = await validator.ValidateRequestAsync(parameters, client);

            result.IsError.Should().BeTrue();
            result.Error.Should().Be(Constants.TokenErrors.InvalidGrant);
        }