public async Task ReceiveAsync(AuthenticationTokenReceiveContext context)
        {

            var allowedOrigin = context.OwinContext.Get<string>("as:clientAllowedOrigin");
            context.OwinContext.Response.Headers.Add("Access-Control-Allow-Origin", new[] { allowedOrigin });

            string hashedTokenId = Helper.GetHash(context.Token);

            using (RefreshTokenRepository _repo = new RefreshTokenRepository())
            {
                var refreshToken = await _repo.FindRefreshToken(hashedTokenId);

                if (refreshToken != null)
                {
                    //Get protectedTicket from refreshToken class
                    context.DeserializeTicket(refreshToken.ProtectedTicket);
                    var result = await _repo.RemoveRefreshToken(hashedTokenId);
                }
            }
        }
        public async Task CreateAsync(AuthenticationTokenCreateContext context)
        {
            var clientid = context.Ticket.Properties.Dictionary["as:client_id"];

            if (string.IsNullOrEmpty(clientid))
            {
                return;
            }

            var refreshTokenId = Guid.NewGuid().ToString("n");

            using (RefreshTokenRepository _repo = new RefreshTokenRepository())
            {
                var refreshTokenLifeTime = context.OwinContext.Get<string>("as:clientRefreshTokenLifeTime");

                var token = new RefreshToken()
                {
                    Id = Helper.GetHash(refreshTokenId),
                    ClientId = clientid,
                    Subject = context.Ticket.Identity.Name,
                    IssuedUtc = DateTime.UtcNow,
                    ExpiresUtc = DateTime.UtcNow.AddMinutes(Convert.ToDouble(refreshTokenLifeTime))
                };

                context.Ticket.Properties.IssuedUtc = token.IssuedUtc;
                context.Ticket.Properties.ExpiresUtc = token.ExpiresUtc;

                token.ProtectedTicket = context.SerializeTicket();

                var result = await _repo.AddRefreshToken(token);

                if (result)
                {
                    context.SetToken(refreshTokenId);
                }

            }
        }
        public override Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
        {
            // Resource owner password credentials does not provide a client ID.
            //if (context.ClientId == null)
            //{
            //    context.Validated();
            //}

            //return Task.FromResult<object>(null);

            string clientId = string.Empty;
            string clientSecret = string.Empty;
            Client client = null;

            if (!context.TryGetBasicCredentials(out clientId, out clientSecret))
            {
                context.TryGetFormCredentials(out clientId, out clientSecret);
            }

            if (context.ClientId == null)
            {
                //Remove the comments from the below line context.SetError, and invalidate context 
                //if you want to force sending clientId/secrects once obtain access tokens. 
                context.Validated();
                //context.SetError("invalid_clientId", "ClientId should be sent.");
                return Task.FromResult<object>(null);
            }


            using (RefreshTokenRepository _repo = new RefreshTokenRepository())
            {
                client = _repo.FindClient(context.ClientId);
            }

            if (client == null)
            {
                context.SetError("invalid_clientId", string.Format("Client '{0}' is not registered in the system.", context.ClientId));
                return Task.FromResult<object>(null);
            }

            if (client.ApplicationType == Models.ApplicationTypes.NativeConfidential)
            {
                if (string.IsNullOrWhiteSpace(clientSecret))
                {
                    context.SetError("invalid_clientId", "Client secret should be sent.");
                    return Task.FromResult<object>(null);
                }
                else
                {
                    if (client.Secret != Helper.GetHash(clientSecret))
                    {
                        context.SetError("invalid_clientId", "Client secret is invalid.");
                        return Task.FromResult<object>(null);
                    }
                }
            }

            if (!client.Active)
            {
                context.SetError("invalid_clientId", "Client is inactive.");
                return Task.FromResult<object>(null);
            }

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

            context.Validated();
            return Task.FromResult<object>(null);
        }