如何在identity server 3中为Sustainsys外部提供程序设置acr值

我有 Idsvr3 https://github.com/Sustainsys/Saml2 我跟着 sample here

现在,当用户访问客户机应用程序时,他将被重定向到login页面,该页面显示用于本地登录的userid/password文本框以及重定向到外部提供程序的按钮。

我想改变这种行为。我希望用户直接转到外部登录基于某些条件。我已经 read that 我可以将所需的登录提供程序传递给 acr_values IdSvr3将直接转到外部提供商。

以下是我如何注册外部提供商 IdSvr3 (注意为了简洁起见,删除了一些代码)

public class Startup
{
    public void Configuration(IAppBuilder app)
    {
        app.Map("/identity", idsrvApp =>
        {
            var identityServerOptions = new IdentityServerOptions
            {
                AuthenticationOptions = new AuthenticationOptions()
                {                        
                }
                .Configure(ConfigureIdentityProviders),                    
            };

            idsrvApp.UseIdentityServer(identityServerOptions);
        });            
    }

    private void ConfigureIdentityProviders(IAppBuilder app, string signInAsType)
    {                           
            // SAML2
            var options = new Saml2AuthenticationOptions(false)
            {
                SPOptions = new SPOptions
                {
                    EntityId = new EntityId("https://localhost:44300/IdSrv3/Saml2"),
                },
                SignInAsAuthenticationType = signInAsType,
                Caption = "SAML2p"
            };

            UseIdSrv3LogoutOnFederatedLogout(app, options);

            options.SPOptions.ServiceCertificates.Add(new X509Certificate2(
                AppDomain.CurrentDomain.SetupInformation.ApplicationBase + "/App_Data/Sustainsys.Saml2.Tests.pfx"));

            options.IdentityProviders.Add(new IdentityProvider(
                new EntityId("https://stubidp.sustainsys.com/Metadata"),
                options.SPOptions)
            {
                LoadMetadata = true
            });

            app.UseSaml2Authentication(options);            
    }
}

这里是客户端应用程序启动

 public class Startup
    {
        public void Configuration(IAppBuilder app)
        {            
            app.UseCookieAuthentication(CK);

            app.UseOpenIdConnectAuthentication(new OpenIdConnectAuthenticationOptions
            {
                Authority = "https://localhost:44300/identity",
                Scope = "openid profile email",
                ClientId = "XXXXXXXXXXXXXXX",
                RedirectUri = "http://localhost:36102/",
                ResponseType = "id_token",
                SignInAsAuthenticationType = "Cookies",               

                Notifications = new OpenIdConnectAuthenticationNotifications
                {                    
                    RedirectToIdentityProvider = (n) =>
                    {
                        if (n.ProtocolMessage.RequestType == OpenIdConnectRequestType.AuthenticationRequest)
                        {
                           if(SomeCondition == true)
                           {
                              n.ProtocolMessage.AcrValues = "idp:saml2";
                           }
                        }

                        return Task.FromResult(0);
                    }
                }                
            });
        }        
    }

但是,identity server抛出错误 External login error: provider requested saml2 is not a configured external provider

有效名称是什么 Sustainsys/Saml2 提供程序及其配置位置?