[Preview 5] Customize the Blazor WASM auth user (#17926)

Author: guardrex

aspnetcore/security/blazor/webassembly/additional-scenarios.md

@@ -395,6 +395,71 @@ The `RemoteAuthenticatorView` has one fragment that can be used per authenticati
 | `authentication/profile`         | `<UserProfile>`         |
 | `authentication/register`        | `<Registering>`         |
 
+## Customize the user
+
+Users bound to the app can be customized. In the following example, all authenticated users receive an `amr` claim for each of the user's authentication methods.
+
+Create a class that extends the `RemoteUserAccount` class:
+
+```csharp
+using System.Text.Json.Serialization;
+using Microsoft.AspNetCore.Components.WebAssembly.Authentication;
+
+public class OidcAccount : RemoteUserAccount
+{
+    [JsonPropertyName("amr")]
+    public string[] AuthenticationMethod { get; set; }
+}
+```
+
+Create a factory that extends `AccountClaimsPrincipalFactory<TAccount>`:
+
+```csharp
+using System.Security.Claims;
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Components;
+using Microsoft.AspNetCore.Components.WebAssembly.Authentication;
+using Microsoft.AspNetCore.Components.WebAssembly.Authentication.Internal;
+
+public class CustomAccountFactory 
+    : AccountClaimsPrincipalFactory<OidcAccount>
+{
+    public AccountClaimsPrincipalFactory(NavigationManager navigationManager, 
+        IAccessTokenProviderAccessor accessor) : base(accessor)
+    {
+    }
+  
+    public async override ValueTask<ClaimsPrincipal> CreateUserAsync(
+        OidcAccount account, RemoteAuthenticationUserOptions options)
+    {
+        var initialUser = await base.CreateUserAsync(account, options);
+        
+        if (initialUser.Identity.IsAuthenticated)
+        {
+            foreach (var value in account.AuthenticationMethod)
+            {
+                ((ClaimsIdentity)initialUser.Identity)
+                    .AddClaim(new Claim("amr", value));
+            }
+        }
+           
+        return initialUser;
+    }
+}
+```
+
+Register services to use the `CustomAccountFactory`:
+
+```csharp
+using Microsoft.AspNetCore.Components.WebAssembly.Authentication;
+
+...
+
+builder.Services.AddApiAuthorization<RemoteAuthenticationState, OidcAccount>()
+    .AddAccountClaimsPrincipalFactory<RemoteAuthenticationState, OidcAccount, 
+        CustomAccountFactory>();
+```
+
 ## Support prerendering with authentication
 
 After following the guidance in one of the hosted Blazor WebAssembly app topics, use the following instructions to create an app that: