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://xp0identityserver.dev.local/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;
    }
  }
}

Package Manager Console commands

Install-Package Sitecore.Plugin.IdentityProviders -Version 5.1.1 -Source https://sitecore.myget.org/F/sc-identity/api/v3/index.json
Install-Package IdentityServer4 -Version 2.3.2 
Install-Package Sustainsys.Saml2.AspNetCore2 -Version 2.8.0

Saml2Configuration.xml

<?xml version="1.0" encoding="utf-8"?>
<Settings>
  <Sitecore>
    <ExternalIdentityProviders>
      <IdentityProviders>
        <Saml2Configuration type="Sitecore.Plugin.IdentityProviders.IdentityProvider, Sitecore.Plugin.IdentityProviders">
          <AuthenticationScheme>Saml2</AuthenticationScheme>
          <DisplayName>Saml2 SSO</DisplayName>
          <Enabled>true</Enabled>
          <ClaimsTransformations>
            <ClaimsTransformation1 type="Sitecore.Plugin.IdentityProviders.DefaultClaimsTransformation, Sitecore.Plugin.IdentityProviders">
              <SourceClaims>
                <Claim1 type="http://schemas.xmlsoap.org/ws/2005/05/identity/claims/upn" />
              </SourceClaims>
              <NewClaims>
                <Claim1 type="email" />
              </NewClaims>
            </ClaimsTransformation1 >
            <ClaimsTransformation2 type="Sitecore.Plugin.IdentityProviders.DefaultClaimsTransformation, Sitecore.Plugin.IdentityProviders">
              <SourceClaims>
                <Claim1 type="http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress" />
              </SourceClaims>
              <NewClaims>
                <Claim1 type="email" />
              </NewClaims>
            </ClaimsTransformation2>
            <AuthorRule type="Sitecore.Plugin.IdentityProviders.DefaultClaimsTransformation, Sitecore.Plugin.IdentityProviders">
              <SourceClaims>
                <Claim1 type="http://schemas.microsoft.com/ws/2008/06/identity/claims/role" value="Author" />
              </SourceClaims>
              <NewClaims>
                <Claim1 type="role" value="sitecore\Author" />
              </NewClaims>
            </AuthorRule>
            <AdminRule  type="Sitecore.Plugin.IdentityProviders.DefaultClaimsTransformation, Sitecore.Plugin.IdentityProviders">
              <SourceClaims>
                <Claim1 type="http://schemas.microsoft.com/ws/2008/06/identity/claims/role" value="Administrator" />
              </SourceClaims>
              <NewClaims>
                <Claim1 type="http://www.sitecore.net/identity/claims/isAdmin" value="true"/>
              </NewClaims>
            </AdminRule>
          </ClaimsTransformations>
        </Saml2Configuration>
      </IdentityProviders>
    </ExternalIdentityProviders>
  </Sitecore>
</Settings>

Sitecore.Plugin.manifest

<?xml version="1.0" encoding="utf-8"?>
<SitecorePlugin PluginName="SitecoreIdentitySamlDemo" AssemblyName="SitecoreIdentitySamlDemo" Version="1.0.0">
  <Dependencies>
    <Dependency name="Sitecore.Plugin.IdentityProviders">5.1.1</Dependency>
  </Dependencies>
  <Tags />
</SitecorePlugin>

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