Configure auth

Skill dotnet/skills/plugins/dotnet-blazor/skills/configure-auth

Repository for skills to assist AI coding agents with .NET and C#

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npx -y skills add dotnet/skills --skill configure-auth

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Add authentication and authorization to a Blazor Web App, accounting for the app's render mode. USE WHEN the user needs [Authorize] on pages, AuthorizeView, role or policy-based access, login/logout Identity pages, or AuthenticationStateProvider. Also USE WHEN auth state is null after WebAssembly loads, SignInManager throws in an interactive component, <NotAuthorized> content never renders in static SSR, or HttpContext.User is null in an interactive component. DO NOT USE for general component authoring (see author-component), for prerendering concerns unrelated to auth (see support-prerendering), or for managing non-auth cascading state (see coordinate-components).

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SKILL.md

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Configure Auth

Step 1 — Read AGENTS.md

Read AGENTS.md at the workspace root for the project's interactivity mode and scope before making changes.

Step 2 — Register auth services in Program.cs

// Program.cs (server project)
builder.Services.AddCascadingAuthenticationState();
builder.Services.AddAuthorization();

For ASP.NET Core Identity add the Identity services:

builder.Services.AddAuthentication(options =>
{
    options.DefaultScheme = IdentityConstants.ApplicationScheme;
    options.DefaultSignInScheme = IdentityConstants.ExternalScheme;
})
.AddIdentityCookies();

builder.Services.AddIdentityCore<ApplicationUser>()
    .AddRoles<IdentityRole>()
    .AddEntityFrameworkStores<ApplicationDbContext>()
    .AddSignInManager()
    .AddDefaultTokenProviders();

Step 3 — Wire App.razor for auth and render mode

The App.razor component must use AuthorizeRouteView and conditionally apply the render mode so that pages excluded from interactive routing render statically.

<!DOCTYPE html>
<html>
<head>
    <HeadOutlet @rendermode="RenderModeForPage" />
</head>
<body>
    <Routes @rendermode="RenderModeForPage" />
    <script src="_framework/blazor.web.js"></script>
</body>
</html>

@code {
    [CascadingParameter]
    public HttpContext HttpContext { get; set; } = default!;

    private IComponentRenderMode? RenderModeForPage =>
        HttpContext.AcceptsInteractiveRouting()
            ? InteractiveServer   // replace with the app's render mode
            : null;
}

In Routes.razor (or wherever the router lives), use AuthorizeRouteView:

<Router AppAssembly="typeof(Program).Assembly">
    <Found Context="routeData">
        <AuthorizeRouteView RouteData="routeData"
                            DefaultLayout="typeof(Layout.MainLayout)">
            <NotAuthorized>
                @if (context.User.Identity?.IsAuthenticated != true)
                {
                    <RedirectToLogin />
                }
                else
                {
                    <p>You are not authorized to access this resource.</p>
                }
            </NotAuthorized>
        </AuthorizeRouteView>
        <FocusOnNavigate RouteData="routeData" Selector="h1" />
    </Found>
</Router>

Step 4 — Protect pages and components

[Authorize] attribute on pages

@page "/admin"
@attribute [Authorize]

With roles or policies:

@attribute [Authorize(Roles = "Admin")]
@attribute [Authorize(Policy = "RequireManager")]

AuthorizeView for conditional UI

<AuthorizeView>
    <Authorized>Welcome, @context.User.Identity?.Name!</Authorized>
    <NotAuthorized><a href="Account/Login">Log in</a></NotAuthorized>
</AuthorizeView>

Role/policy variants:

<AuthorizeView Roles="Admin,Manager">
    <Authorized>Admin content here</Authorized>
</AuthorizeView>

Access auth state in code

[CascadingParameter]
private Task<AuthenticationState>? AuthState { get; set; }

protected override async Task OnInitializedAsync()
{
    if (AuthState is not null)
    {
        var state = await AuthState;
        var isAdmin = state.User.IsInRole("Admin");
    }
}

Step 5 — Identity pages must stay static SSR

SignInManager and UserManager use HttpContext internally and throw in interactive components. Identity pages (login, register, manage) must render as static SSR.

In a globally interactive app, mark every Identity page:

@page "/Account/Login"
@attribute [ExcludeFromInteractiveRouting]

This forces a full-page navigation (exits the interactive circuit) so the page renders through the static SSR pipeline with a real HttpContext.

App.razor must use AcceptsInteractiveRouting() (Step 3) to return null for these pages — otherwise the framework still tries to render them interactively.

In a per-page app, Identity pages are static by default (no @rendermode directive), so [ExcludeFromInteractiveRouting] is not needed.

Step 6 — Auth state in WebAssembly / Auto mode

WebAssembly components run in the browser and have no HttpContext. Auth state must be serialized from the server during prerendering and deserialized on the client.

Server Program.cs:

builder.Services.AddAuthenticationStateSerialization();

Client .Client/Program.cs:

builder.Services.AddAuthenticationStateDeserialization();

Without these calls, Task<AuthenticationState> resolves to an anonymous user after WebAssembly takes over from prerendering.

AddAuthenticationStateSerialization accepts options to include role and claim data:

builder.Services.AddAuthenticationStateSerialization(options =>
    options.SerializeAllClaims = true);

Render Mode × Auth Matrix

Render mode	HttpContext.User	SignInManager	Auth state source	Key requirement
Static SSR	Available	Works	Server pipeline	Use middleware for redirects, `<NotAuthorized>` does NOT render
Server (interactive)	NOT available	Throws	`CascadingAuthenticationState`	Use `[Authorize]` + `AuthorizeView`, not `HttpContext`
WebAssembly	NOT available	Throws	Serialized from server	`AddAuthenticationStateSerialization` / `Deserialization`
Auto	NOT available after WASM	Throws	Serialized from server	Same as WebAssembly; register in both Program.cs files

Common Mistakes

Mistake	Symptom	Fix
Using `HttpContext.User` in interactive component	Null or stale claims	Use `[CascadingParameter] Task<AuthenticationState>`
`SignInManager` in interactive component	`InvalidOperationException`	Move to static SSR page with `[ExcludeFromInteractiveRouting]`
Missing `AddAuthenticationStateSerialization`	Anonymous user after WASM loads	Add to server Program.cs; add `Deserialization` to client Program.cs
`<NotAuthorized>` in static SSR layout	Content never shown	Static SSR uses middleware pipeline; redirect via `LoginPath` or `RedirectToLogin` component
Global interactivity without `AcceptsInteractiveRouting`	Identity pages crash	Add `AcceptsInteractiveRouting()` check in App.razor (Step 3)
Missing `AddCascadingAuthenticationState()`	`Task<AuthenticationState>` is null	Register in Program.cs (Step 2)