idsrv4 SAML

appsettings.json

"SAML": {
    "$schema": "https://www.componentspace.com/schemas/saml-config-schema-v1.0.json",
    "Configurations": [
      {
        "LocalIdentityProviderConfiguration": {
          "Name": "https://IdentityServer4",
          "Description": "IdentityServer4",
          "SingleSignOnServiceUrl": "http://localhost:5000/SAML/SingleSignOnService",
          "SingleLogoutServiceUrl": "http://localhost:5000/SAML/SingleLogoutService",
          "ArtifactResolutionServiceUrl": "http://localhost:5000/SAML/ArtifactResolutionService",
          "LocalCertificates": [
            {
              "FileName": "certificates/idp.pfx",
              "Password": "password"
            }
          ]
        },
        "PartnerServiceProviderConfigurations": [
          {
            "Name": "https://ExampleServiceProvider",
            "Description": "Example Service Provider",
            "WantAuthnRequestSigned": true,
            "SignSamlResponse": true,
            "AssertionConsumerServiceUrl": "https://localhost:44360/SAML/AssertionConsumerService",
            "SingleLogoutServiceUrl": "https://localhost:44360/SAML/SingleLogoutService",
            "ArtifactResolutionServiceUrl": "https://localhost:44360/SAML/ArtifactResolutionService",
            "PartnerCertificates": [
              {
                "FileName": "certificates/sp.cer"
              }
            ]
          }
        ]
      }
    ]
  }

Configure.cs

app.UseIdentityServer();

// Use SAML middleware.
app.UseSaml();
// Specify the display name and return URL for logout.
app.Use(async (context, next) =>
{
    if (context.Request.Path.Value.Equals("/Account/Logout", StringComparison.OrdinalIgnoreCase) &&
         string.IsNullOrEmpty(context.Request.Query["logoutId"]))
    {
        var identityServerInteractionService =
            context.RequestServices.GetRequiredService<IIdentityServerInteractionService>();
        var logoutMessageStore =
            context.RequestServices.GetRequiredService < IMessageStore < LogoutMessage >> ();
        var logoutMessage = new Message<LogoutMessage>(new LogoutMessage
        {
            ClientName = "SAML Service Provider",
            PostLogoutRedirectUri = "/SAML/SingleLogoutServiceCompletion"
        },
        DateTime.UtcNow);
        var logoutId = await logoutMessageStore.WriteAsync(logoutMessage);
        context.Request.QueryString = context.Request.QueryString.Add("logoutId", logoutId);
    }
    await next();
});

app.UseStaticFiles();
app.UseMvcWithDefaultRoute();

ConfigureServices.cs

...

services.AddExternalIdentityProviders();

// Add SAML SSO services.
//services.AddSaml(Configuration.GetSection("SAML"));
services.AddSaml(_config.GetSection("SAML"));

// Add SAML Middleware
services.AddSamlMiddleware();

return services.BuildServiceProvider(validateScopes: true);

https://medium.com/the-new-control-plane/connecting-identityserver-4-idp-and-the-componentspace-saml-v2-0-for-net-core-stack-2cf851d61ab9