OpenID与SAML 2.0选型咨询：跨域用户场景下如何选择SSO方案

Hey there! Let's break this down clearly since you're new to OpenID and SAML and trying to pick the right SSO fit for your app with cross-domain users (like abc@testdomain.com, xyz@xyzdomain.com).

First, let's clarify: when people talk about "OpenID" these days, they almost always mean OpenID Connect (OIDC)—a modern, JSON-based extension of OAuth 2.0. SAML is an older, XML-based protocol built for enterprise identity scenarios. Here's how they stack up for your cross-domain use case:

SAML #

• Best for: Enterprise-focused apps where users come from corporate domains (e.g., each domain is tied to a company's internal identity system like Active Directory). Most enterprise identity providers (IDPs) like ADFS, Okta's enterprise tier, or Azure AD support SAML out of the box.
• Pros: Mature, widely adopted in enterprise environments, strong support for identity assertions between trusted parties.
• Cons: Heavier XML-based protocol, less flexible for consumer-facing or modern web/mobile apps.

OpenID Connect (OIDC) #

• Best for: Multi-tenant SaaS apps, consumer-facing apps, or scenarios where users might log in via a mix of corporate and consumer IDPs (like Google, Facebook, or your custom-built IDP). It’s lightweight and designed for modern app architectures.
• Pros: JSON-based, easier to integrate with frontends, supports both server-side and client-side flows, and is the de facto standard for modern SSO.
• Cons: Less common in legacy enterprise environments compared to SAML.

Quick Recommendation #

If your users are primarily from corporate domains with existing enterprise ID systems, go with SAML. If you’re building a flexible, modern app that needs to support a variety of identity sources (corporate or consumer), OIDC is the better pick.

Both protocols have solid support in .NET MVC. Here’s a starting point for each:

OpenID Connect (OIDC) #

Use ASP.NET Core’s built-in OIDC middleware—no third-party libraries needed for most cases:

1. Configure Services (in Program.cs for .NET 6+ or Startup.cs for older versions):

   builder.Services.AddAuthentication(options =>
   {
       options.DefaultScheme = CookieAuthenticationDefaults.AuthenticationScheme;
       options.DefaultChallengeScheme = OpenIdConnectDefaults.AuthenticationScheme;
   })
   .AddCookie()
   .AddOpenIdConnect(options =>
   {
       // Replace with your IDP details (e.g., Auth0, Okta, Azure AD)
       options.ClientId = "your-client-id";
       options.ClientSecret = "your-client-secret";
       options.Authority = "https://your-idp-domain/";
       
       options.ResponseType = "code"; // Authorization Code Flow (most secure for server-side apps)
       options.Scope.Add("openid"); // Required OIDC scope
       options.Scope.Add("profile"); // Get user profile data
       options.Scope.Add("email"); // Get user email
       
       options.SaveTokens = true; // Persist tokens for later use
   });
   
   // Don't forget to add authorization middleware
   app.UseAuthentication();
   app.UseAuthorization();
   

2. Protect Controllers/Actions
   Add the [Authorize] attribute to any controller or action that requires login:

   [Authorize]
   public class HomeController : Controller
   {
       public IActionResult Index()
       {
           // Access user claims via User.Claims
           var userEmail = User.FindFirstValue(ClaimTypes.Email);
           return View();
       }
   }
   

When users visit an authorized route, they’ll automatically be redirected to your IDP’s login page, and redirected back to your app after authentication.

SAML #

For SAML, use the popular ITfoxtec.Identity.Saml2 library—it’s tailored for .NET apps:

1. Install the NuGet Package
   Run this in the Package Manager Console:

   Install-Package ITfoxtec.Identity.Saml2.Mvc
   

2. Configure Services

   builder.Services.AddSaml2(options =>
   {
       // Configure your Service Provider (SP) details
       options.SPOptions = new SPOptions
       {
           EntityId = new EntityId("https://your-app-domain/saml2"),
           ReturnUrl = new Uri("https://your-app-domain/Home/Index"),
       };
   
       // Add your Identity Provider (IDP) metadata
       options.IdentityProviders.Add(new IdentityProvider(
           new EntityId("https://your-idp-domain/saml2/idp"), options.SPOptions)
       {
           LoadMetadata = true,
           MetadataLocation = "https://your-idp-domain/saml2/idp/metadata",
       });
   });
   
   // Add auth middleware
   app.UseAuthentication();
   app.UseAuthorization();
   

3. Add a SAML Controller
   Handle login, callback, and logout flows:

   public class SamlController : Controller
   {
       private readonly Saml2Configuration _saml2Config;
       private readonly Saml2AuthnResponse _saml2AuthnResponse;
   
       public SamlController(Saml2Configuration saml2Config, Saml2AuthnResponse saml2AuthnResponse)
       {
           _saml2Config = saml2Config;
           _saml2AuthnResponse = saml2AuthnResponse;
       }
   
       // Initiate SAML login
       public IActionResult Login()
       {
           var binding = new Saml2RedirectBinding();
           binding.SetRelayState(Url.Action("Index", "Home"));
           return binding.Bind(new Saml2AuthnRequest(_saml2Config)).ToActionResult();
       }
   
       // Handle SAML response from IDP
       public async Task<IActionResult> AssertionConsumerService()
       {
           await _saml2AuthnResponse.ReadSamlResponseAsync(Request.ToGenericHttpRequest());
   
           if (_saml2AuthnResponse.Status != Saml2StatusCodes.Success)
           {
               throw new AuthenticationException($"SAML login failed: {_saml2AuthnResponse.Status}");
           }
   
           // Create a ClaimsPrincipal from the SAML response
           var claimsPrincipal = _saml2AuthnResponse.CreatePrincipal();
           await HttpContext.SignInAsync(CookieAuthenticationDefaults.AuthenticationScheme, claimsPrincipal);
   
           return Redirect(_saml2AuthnResponse.RelayState);
       }
   }
   

You can then add a login button pointing to /Saml/Login to trigger the SAML flow.

内容的提问来源于stack exchange，提问作者Dhaval Pankhaniya