How to use Azure AD Saml2 authentication for SSO in .NET Core 3.1

Question

I am using Sustainsys.Saml2 for Azure AD Saml2 authentication in .NET Core 3.1.I can able to authenticate, but after the login page is redirected to this address https://localhost:44378/Saml2/Acs.system automatically adding "/Saml2/Acs".I could not find the correct tutorial for using this. I need to use the reply URL properly. once successfully authenticated I need to call a particular controller.

// Startup.cs class

services.AddAuthentication(sharedOptions =>
            {
                sharedOptions.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;
                sharedOptions.DefaultSignInScheme = CookieAuthenticationDefaults.AuthenticationScheme;
               sharedOptions.DefaultChallengeScheme = "Saml2";
            })
            .AddSaml2(options =>
            {
               options.SPOptions.EntityId = new EntityId("https://localhost:44378/Saml2");
                options.IdentityProviders.Add(
                new IdentityProvider(
                  new EntityId("https://sts.windows.net/9e5692e4-bd0a-414d-8b61-98f59dab156e/"), options.SPOptions)
                {
                    MetadataLocation = "https://login.microsoftonline.com/7e5692e4-bgf0a-4148-8b61-98f59dab156e/federationmetadata/2007-06/federationmetadata.xml?appid=1729db2f-0156-41cb-b4e3-d54bed555b85"
                });
            })
            .AddCookie();

            services.AddMvc(options =>
            {
                var policy = new AuthorizationPolicyBuilder()
                    .RequireAuthenticatedUser()
                    .Build();
                options.Filters.Add(new AuthorizeFilter(policy));
            });

error msg is

This localhost page can't be found No webpage was found for the web address: https://localhost:44378/Saml2/Acs HTTP ERROR 404

Answer 1

You need to add app.UseAuthentication(); under your Configure method in the Startup class.

public class Startup
{
    public void Configure(IApplicationBuilder app)
    {
        app.UseAuthentication();
    }
}

This will enable the SAML2 middleware in your application.