public async Task <bool> InvokeReturnPathAsync()
        {
            var model = await AuthenticateAsync();

            if (model == null)
            {
                _logger.WriteWarning("Invalid return state, unable to redirect.");
                Response.StatusCode = 500;
                return(true);
            }

            var context = new YahooReturnEndpointContext(Context, model)
            {
                SignInAsAuthenticationType = Options.SignInAsAuthenticationType,
                RedirectUri = model.Properties.RedirectUri
            };

            model.Properties.RedirectUri = null;

            await Options.Provider.ReturnEndpoint(context);

            if (context.SignInAsAuthenticationType != null && context.Identity != null)
            {
                var signInIdentity = context.Identity;
                if (!string.Equals(signInIdentity.AuthenticationType, context.SignInAsAuthenticationType, StringComparison.Ordinal))
                {
                    signInIdentity = new ClaimsIdentity(signInIdentity.Claims, context.SignInAsAuthenticationType, signInIdentity.NameClaimType, signInIdentity.RoleClaimType);
                }
                Context.Authentication.SignIn(context.Properties, signInIdentity);
            }

            if (context.IsRequestCompleted || context.RedirectUri == null)
            {
                return(context.IsRequestCompleted);
            }
            if (context.Identity == null)
            {
                // add a redirect hint that sign-in failed in some way
                context.RedirectUri = WebUtilities.AddQueryString(context.RedirectUri, "error", "access_denied");
            }
            Response.Redirect(context.RedirectUri);
            context.RequestCompleted();

            return(context.IsRequestCompleted);
        }
 /// <summary>
 /// Invoked prior to the <see cref="System.Security.Claims.ClaimsIdentity"/> being saved in a local cookie and the browser being redirected to the originally requested URL.
 /// </summary>
 /// <param name="context"></param>
 /// <returns>A <see cref="Task"/> representing the completed operation.</returns>
 public virtual Task ReturnEndpoint(YahooReturnEndpointContext context)
 {
     return(OnReturnEndpoint(context));
 }
 /// <summary>
 /// Invoked prior to the <see cref="System.Security.Claims.ClaimsIdentity"/> being saved in a local cookie and the browser being redirected to the originally requested URL.
 /// </summary>
 /// <param name="context"></param>
 /// <returns>A <see cref="Task"/> representing the completed operation.</returns>
 public virtual Task ReturnEndpoint(YahooReturnEndpointContext context)
 {
     return OnReturnEndpoint(context);
 }