Blazor using Azure AD authentication allowing anonymous access

Question

I'm currently writing a (Server side) Blazor application that includes the default AzureAD Authentication.

This works well for authenticated users - challenging on the entrance ( _Host.cshtml ) file, redirecting and then back once authenticated.

I need to have a couple of pages not requiring authentication - I don't want the user being challenged and redirected to Microsoft.

What is the correct way to do this? I have experimented with the AllowAnonymousAttribute , the AllowAnonymousToPage razor pages options, nothing seems to stop the challenge.

Any help would be greatly appreciated!

Below is my setup for Authentication (ConfigureServices):

public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthentication(AzureADDefaults.AuthenticationScheme)
        .AddAzureAD(options => Configuration.Bind("AzureAd", options));

    services.AddControllersWithViews(options =>
{
    var policy = new AuthorizationPolicyBuilder()
        .RequireAuthenticatedUser()
        .Build();
    options.Filters.Add(new AuthorizeFilter(policy));
});

    services.AddRazorPages();
    services.AddServerSideBlazor();
    services.AddTelerikBlazor();
}

And then the appropriate part in Configure:

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

app.UseEndpoints(endpoints =>
{
    endpoints.MapControllers();
    endpoints.MapBlazorHub();
    endpoints.MapFallbackToPage("/_Host");
});

Answer 1

I found what I had to do was add the following to _Hosts.cshtml

@using Microsoft.AspNetCore.Authorization
@attribute [AllowAnonymous]

Once I did this authorization was no longer required on any of the pages by default and I could then add it to the pages where I wanted to require it.

For example if you wanted to secure the Counter.razor page just add an Authorize attribute to the top:

@attribute [Authorize]

So now if you tried to access the counter page you will get a Not authorized message.

If you want to remove the counter link when the user is not logged in modify the NavMenu.razor and surround the Counter link with an <AuthorizeView> </AuthorizeView> as so:

<AuthorizeView>
    <li class="nav-item px-3">
        <NavLink class="nav-link" href="counter">
            <span class="oi oi-plus" aria-hidden="true"></span> Counter
        </NavLink>
    </li>
</AuthorizeView> 

Ideally I would have liked to just opt out of authorization for the index page and have everything else secured by default but I could not find a way to get that to work. If I tried adding the @attribute [AllowAnonymous] to the Index.razor page it seemed to ignore it.