public override async Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
        {
            var userManager = GebruikerManager.Create(System.Web.HttpContext.Current.GetOwinContext().Get <AppBuilderProvider>().Get().GetDataProtectionProvider());

            Gebruiker user = await userManager.FindAsync(context.UserName, context.Password);

            if (user == null)
            {
                context.SetError("invalid_grant", "The user name or password is incorrect.");
                return;
            }

            ClaimsIdentity oAuthIdentity = await user.GenerateUserIdentityAsync(userManager,
                                                                                OAuthDefaults.AuthenticationType);

            ClaimsIdentity cookiesIdentity = await user.GenerateUserIdentityAsync(userManager,
                                                                                  CookieAuthenticationDefaults.AuthenticationType);

            AuthenticationProperties properties = CreateProperties(user.UserName);
            AuthenticationTicket     ticket     = new AuthenticationTicket(oAuthIdentity, properties);

            context.Validated(ticket);
            context.Request.Context.Authentication.SignIn(cookiesIdentity);
        }