Tutorial: Configure an ASP.NET Core web app for authorization and authentication

In this tutorial, you add the authentication and authorization elements to an ASP.NET Core web app. In the previous tutorial, you created an ASP.NET Core project and configured it for authentication.

In this tutorial:

• Completion of the prerequisites and steps in Tutorial: Set up an ASP.NET Core web app that authenticates users.

The HomeController.cs and Program.cs files need to be modified to add the authentication and authorization elements to the ASP.NET Core web app. This includes managing the home page, adding correct namespaces and configuring sign-in.

The home page of the application needs to have the capability to authorize the user. The Microsoft.AspNetCore.Authorization namespace provides the classes and interfaces to implement authorization to the web app. The [Authorize] attribute is used to specify that only authenticated users can use the web app.

1. In your web app, open Controllers/HomeController.cs, and add the following snippet to the top of the file:

   using System.Diagnostics;
   using Microsoft.AspNetCore.Authorization;
   using Microsoft.AspNetCore.Mvc;
   using dotnetcore_webapp.Models;
   

2. Add the [Authorize] attribute above the HomeController class definition, as shown in the following snippet:

   [Authorize]
   public class HomeController : Controller
   {
   ...
   

The Program.cs file is the entry point of the application, and needs to be modified to add authentication and authorization to the web app. Services need to be added to allow the app to use the settings defined in appsettings.json for authentication.

1. Add the following namespaces to the top of the file.

   using Microsoft.AspNetCore.Authentication.OpenIdConnect;
   using Microsoft.AspNetCore.Authorization;
   using Microsoft.AspNetCore.Mvc.Authorization;
   using Microsoft.Identity.Web;
   using Microsoft.Identity.Web.UI;
   using System.IdentityModel.Tokens.Jwt;
   

2. Next, add the Microsoft Identity Web app authentication service, which configures the app to use Microsoft Identity for authentication.

   // Add services to the container.
   builder.Services.AddControllersWithViews();
   
   // This is required to be instantiated before the OpenIdConnectOptions starts getting configured.
   // By default, the claims mapping will map claim names in the old format to accommodate older SAML applications.
   // This flag ensures that the ClaimsIdentity claims collection will be built from the claims in the token
   JwtSecurityTokenHandler.DefaultMapInboundClaims = false;
   
   // Sign-in users with the Microsoft identity platform
   builder.Services.AddAuthentication(OpenIdConnectDefaults.AuthenticationScheme)
       .AddMicrosoftIdentityWebApp(builder.Configuration)
       .EnableTokenAcquisitionToCallDownstreamApi()
       .AddInMemoryTokenCaches();
   
   builder.Services.AddControllersWithViews(options =>
   {
       var policy = new AuthorizationPolicyBuilder()
           .RequireAuthenticatedUser()
           .Build();
       options.Filters.Add(new AuthorizeFilter(policy));
   }).AddMicrosoftIdentityUI();
   
   

3. Next, the middleware needs to be configured to enable the authentication capabilities. Replace the rest of the code with the following snippet.

   var app = builder.Build();
   
   // Configure the HTTP request pipeline.
   if (!app.Environment.IsDevelopment())
   {
       app.UseExceptionHandler("/Home/Error");
       // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
       app.UseHsts();
   }
   
   app.UseHttpsRedirection();
   app.UseStaticFiles();
   
   app.UseRouting();
   app.UseAuthorization();
   
   app.MapControllerRoute(
       name: "default",
       pattern: "{controller=Home}/{action=Index}/{id?}");
   
   app.Run();
   

The UI needs to be updates to provide a more user-friendly experience for sign-in and sign-out. This section shows how to create a new file that displays navigation items based on the user's authentication status. The code reads the ID token claims to check that the user is authenticated and uses User.Claims to extract ID token claims.

1. Create a new file in Views/Shared and give it the name _LoginPartial.cshtml.

2. Open the file and add the following code for adding the sign in and sign out experience:

   @using System.Security.Principal
   
   <ul class="navbar-nav">
   @if (User.Identity is not null && User.Identity.IsAuthenticated)
   {
           <li class="nav-item">
               <span class="nav-link text-dark">Hello @User.Claims.First(c => c.Type == "preferred_username").Value!</span>
           </li>
           <li class="nav-item">
               <a class="nav-link text-dark" asp-area="MicrosoftIdentity" asp-controller="Account" asp-action="SignOut">Sign out</a>
           </li>
   }
   else
   {
           <li class="nav-item">
               <a class="nav-link text-dark" asp-area="MicrosoftIdentity" asp-controller="Account" asp-action="SignIn">Sign in</a>
           </li>
   }
   </ul>
   

3. Open Views/Shared/_Layout.cshtml and add a reference to _LoginPartial created in the previous step. Place this near the end of the navbar-nav class as shown in the following snippet:

   <div class="navbar-collapse collapse d-sm-inline-flex justify-content-between">
       <ul class="navbar-nav flex-grow-1">
           <li class="nav-item">
               <a class="nav-link text-dark" asp-area="" asp-page="/Index">Home</a>
           </li>
           <li class="nav-item">
               <a class="nav-link text-dark" asp-area="" asp-page="/Privacy">Privacy</a>
           </li>
       </ul>
       <partial name="_LoginPartial" />
   </div>