Authorization in Blazor Applications

In this lesson, you will learn how to synchronize and manage user authorization states effectively across Blazor Server and Blazor WebAssembly environments.

The Blazor Authorization Challenge

When working with Blazor, we deal with two distinct hosting models that treat security differently. In Blazor Server, the application state lives on the server, meaning the AuthenticationStateProvider has direct access to the user's HttpContext. Conversely, in Blazor WebAssembly, the state exists in the browser, requiring us to manage identity via secure tokens. Despite these architectural differences, the goal is consistent: ensuring the UI reflects the user's authorized status without leaking sensitive data.

Bridging the Gap

To manage authorization states, we rely on the AuthenticationStateProvider service. This service acts as the source of truth for the AuthenticationState (which contains the user’s ClaimsPrincipal).

In a standard Blazor application, you wrap your main content in the CascadingAuthenticationState component. This allows any child component to request the current authorization status using CascadingParameter:

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

protected override async Task OnInitializedAsync()
{
    var authState = await AuthStateTask;
    var user = authState.User;

    if (user.Identity.IsAuthenticated)
    {
        // Handle logic for authorized users
    }
}

Server vs. Client Consistency

The critical difference lies in the implementation of the AuthenticationStateProvider.

• Blazor Server: You use the built-in ServerAuthenticationStateProvider, which keeps the state in sync with the server-side session.
• Blazor WebAssembly: You must implement a custom AuthenticationStateProvider that retrieves the user's claims from a local secure storage or an identity token (OIDC).

Regardless of the model, you should always enforce authorization at the "resource" level (e.g., inside your API controllers or service layer), because the Blazor UI only provides a visual representation of the state. Never rely solely on UI-level hiding (AuthorizeView) to protect sensitive logic; always ensure your backend services validate the user's claims independently of the client-side state.

Key Takeaway: Always use a CascadingAuthenticationState to propagate identity, but treat UI-level authorization as a convenience, while enforcing all security constraints at the API or service layer.