Sitecore Identity to Sustainsys Plugin

ConfigureSitecore.cs

using IdentityServer4;
using Microsoft.AspNetCore.Authentication;
using Microsoft.Extensions.DependencyInjection;
using Sustainsys.Saml2;
using Sustainsys.Saml2.Configuration;
using Sustainsys.Saml2.Metadata;
using Sustainsys.Saml2.WebSso;

namespace SitecoreIdentitySamlDemo
{
	public class ConfigureSitecore
	{
		public void ConfigureServices(IServiceCollection services)
		{
			var builder = new AuthenticationBuilder(services);

			builder.AddSaml2("Saml2", "SSO Button Text", options =>
			{
				options.SignInScheme = "idsrv.external";
				options.SignOutScheme = IdentityServerConstants.DefaultCookieAuthenticationScheme;
				options.SPOptions.EntityId = new EntityId("https://testidserver2/Saml2");
				IdentityProvider provider = GetIdentityProvider(options.SPOptions);
				options.IdentityProviders.Add(provider);
			});
		}

		private IdentityProvider GetIdentityProvider(SPOptions options)
		{
			var idp = new IdentityProvider(new EntityId("https://stubidp.sustainsys.com/Metadata"), options);
			idp.Binding = Saml2BindingType.HttpPost;
			idp.LoadMetadata = true;
			return idp;
		}
	}
}

Code examples for this article: https://www.velir.com/ideas/2021/09/22/connecting-sitecore-identity-to-saml-part-1