Authentication and authorization state data in code in blazor

In our previous video we discussed, how to use [Authorize] attribute to authorize access to routable components (i.e components with @page directive). We did this in the component html.

In this video we will discuss, how to obtain authentication and authorization state data in code in blazor.

Cascading AuthenticationState parameter

• Cascading AuthenticationState parameter (Task<AuthenticationState>) provides authentication and authorization state data.
• If the user is not authenticated, the request is redirected to the login page. 
• The return url is also passed as the query string parameter to the login page.
• Upon successful login, the user will be redirected to the page he was trying to access.

public class EditEmployeeBase : ComponentBase
{
    [CascadingParameter]
    private Task<AuthenticationState> authenticationStateTask { get; set; }

    [Inject]
    public NavigationManager NavigationManager { get; set; }

    protected async override Task OnInitializedAsync()
    {
        var authenticationState = await authenticationStateTask;

        if (!authenticationState.User.Identity.IsAuthenticated)
        {
            string returnUrl = WebUtility.UrlEncode($"/editEmployee/{Id}");
            NavigationManager.NavigateTo($"/identity/account/login?returnUrl={returnUrl}");
        }

        // rest of the code
    }
}

Check if authenticated user is in a specific role

if (authenticationState.User.IsInRole("Administrator"))
{
    // Execute Admin logic
}

Check if authenticated user satisfies a specific policy

Task<AuthenticationState> can be combined with IAuthorizationService, to check if a specific aothorization policy is satisfied.

public class EditEmployeeBase : ComponentBase
{
    [CascadingParameter]
    private Task<AuthenticationState> authenticationStateTask { get; set; }

    [Inject]
    private IAuthorizationService AuthorizationService { get; set; }

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

        if ((await AuthorizationService.AuthorizeAsync(user, "admin-policy"))
        .Succeeded)
        {
            // Execute code specific to admin-policy
        }
    }
}