Implementing SAML SSO in .NET 10 MVC Using Microsoft Entra ID

Introduction

Enterprise authentication is rarely about writing code first - it is about establishing trust between systems.

In this article, we will build a complete SAML-based Single Sign-On integration between:

A .NET 10 MVC application (Service Provider)
Microsoft Entra ID (Identity Provider)

Instead of jumping between portals and code randomly, we will follow a structured flow:

Create the MVC application (to generate launch URL)
Configure Microsoft Entra Enterprise Application
Integrate SAML middleware
Test authentication
Implement proper logout
Support both Metadata URL and XML file approach

By the end, you will have a fully working SAML implementation.

Part 1 — Create the MVC Application (We Need the URL First)

Before touching Azure, we need the application's base URL.

Step 1 — Create a New MVC Project

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(Create a new project → ASP.NET Core Web App MVC)

Click:

Create a new project
Select → ASP.NET Core Web App (Model-View-Controller)

Step 2 — Configure Project

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Project name: WebApplicationSamlSso

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Select:

Framework: .NET 10.0 (LTS)

Authentication type: None

Enable HTTPS: ✔

Click Create.

Step 3 — Run the Application Once

Launch the app.

Your HTTPS URL will look like:

https://localhost:7136

This URL is important. (Note: Port could be different)

We will use it in Azure SAML configuration.

Part 2 — Create Enterprise Application in Microsoft Entra

Now we move to:

https://entra.microsoft.com

Step 4 — Navigate to Enterprise Applications

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Path:

Home → Entra ID → Enterprise apps → New application

Step 5 — Create Your Own Application

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Search: Microsoft Entra SAML Toolkit

Click:

Create your own application

Select:

Integrate any other application you don't find in the gallery (Non-gallery)

Click Create.

This creates a Service Principal inside your tenant.

Step 6 — Enable SAML

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Inside the app:

Single sign-on → Select SAML

Step 7 — Configure Basic SAML Settings

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(Overview screen before editing)

Click Edit under Basic SAML Configuration.

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Now configure:

Identifier (Entity ID)

https://localhost:7136

Reply URL (ACS)

https://localhost:7136/Saml2/Acs

Sign On URL

https://localhost:7136

Relay State (Optional)

https://localhost:7136/Home/Privacy

Logout URL

https://localhost:7136/Saml2/Logout

Save changes.

Step 8 — Assign Users

SAML will not work unless users are assigned.

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Go to:

Users and groups → Add user/group

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Select a user → Click Assign.

Without this step, login will fail.

Step 9 — Download Metadata (Optional XML Approach)

Scroll to:

SAML Signing Certificate

Download:

Federation Metadata XML

Now Azure configuration is complete.

Part 3 — Integrate SAML in .NET Application

Step 10 — Install NuGet Package

Screenshot 13.png

Install:

Sustainsys.Saml2.AspNetCore2

Step 11 — Configure Program.cs

Open Program.cs and add:

builder.Services.AddAuthentication(options =>
{
    options.DefaultScheme = "Cookies";
    options.DefaultChallengeScheme = Saml2Defaults.Scheme;
})
.AddCookie()
.AddSaml2(options =>
{
    options.SPOptions.EntityId =
        new EntityId("https://localhost:7136");

    options.IdentityProviders.Add(
        new IdentityProvider(
            new EntityId("https://sts.windows.net/YOUR-TENANT-ID/"),
            options.SPOptions)
        {
            MetadataLocation =
            "https://login.microsoftonline.com/YOUR-TENANT-ID/federationmetadata/2007-06/federationmetadata.xml",
            LoadMetadata = true
        });
});

Ensure:

app.UseAuthentication();
 app.UseAuthorization();

Alternative — Using Downloaded XML File

Instead of metadata URL, you can place XML file inside a folder (e.g., /Saml) and change one line:

MetadataLocation = "Saml/FederationMetadata.xml";

That's the only difference.

Step 12 — Protect a Controller

Add:

[Authorize]
 public IActionResult Privacy()
 {
    return View();
 }

Run:

https://localhost:7136/Home/Privacy

You should be redirected to Microsoft Entra login.

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Step 13 — Implement Proper Logout

Create AccountController:

[Authorize]
[HttpPost]
public IActionResult Logout()
{
    return SignOut(
        new AuthenticationProperties
        {
            RedirectUri = "/"
        },
        "Cookies",
        Saml2Defaults.Scheme
    );
}

This clears:

✔ Application cookie
✔ Entra session

Final Flow Summary

User accesses protected route
App redirects to Entra
Entra authenticates user
Sends signed SAML assertion
App validates and issues cookie
User gains access
Logout clears both sessions