Access AuthenticationState in Blazor Server to update components in a single place

[lonwabogiqwa]

Is there a way that I can use in Blazor to check authentication state in one place such as MainLayout.razor, so that when you are navigating to a component I can invalidate state if token expired? For example if you use OnAfterRenderAsync it is too late because the page has already rendered. I do not want to be repeating the check on every component. So I want to know if there is a lifecycle function that gets called each time you navigate to a component where I can do something like this
var authState = await AuthenticationStateProvider.GetAuthenticationStateAsync();

        if (authState.User.Identity != null && authState.User.Identity.IsAuthenticated == false)
        {
            Logout();
        }
        StateHasChanged();

[SteveSandersonMS]

If you want to share common functionality across all pages, here are a couple of options:

Option 1: Common base class

If you create a C# class that inherits from ComponentBase, then you can make all your .razor components inherit from your custom class via:

@inherits MyCustomBaseClass

Then, in MyCustomBaseClass, you can override lifecycle events like OnInitializedAsync and put your common logic there.

Option 2: In the router

If you don't want to use inheritance, then you could use something like the following in App.razor:

<Router AppAssembly="@typeof(Program).Assembly">
    <Found Context="routeData">
        <MyRoutingMiddleware>
            <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)" />
        </MyRoutingMiddleware>
    </Found>
    <NotFound>
        <LayoutView Layout="@typeof(MainLayout)">
            <p>Sorry, there's nothing at this address.</p>
        </LayoutView>
    </NotFound>
</Router>

All I've added here is MyRoutingMiddleware, which you can define by creating MyRoutingMiddleware.razor containing this:

@if (canShowDestination)
{
    @ChildContent
}
else
{
    <LayoutView Layout="@typeof(MainLayout)">
        <h2>Checking...</h2>
    </LayoutView>
}

@code {
    bool canShowDestination;

    [Parameter] public RenderFragment ChildContent { get; set; }

    protected override async Task OnParametersSetAsync()
    {
        canShowDestination = false;
        await DoTheAsyncThing();
        canShowDestination = true;
    }

    private async Task DoTheAsyncThing()
    {
        // TODO: Whatever async thing you want here
        await Task.Delay(2000);
    }
}

As you can see, every time you navigate this will call DoTheAsyncThing which will do whatever you want before showing the new destination page. If you wanted you could block access to the page or whatever else you like.