bulletboards/ImageBoardServerApp/Shared/MainLayout.razor

@using ImageBoardServerApp.Auth
@inherits LayoutComponentBase
@inject AuthenticationStateProvider authStateProvider 
@inject NavigationManager navManager

<PageTitle>BulletBoard</PageTitle>

<div class="page">
    <div class="sidebar">
        <NavMenu/>
    </div>

    <main>
        <article class="content px-4">
            @Body
        </article>
    </main>
</div>

@code
{

    private string mail { get; set; } = "";

    protected override async Task OnInitializedAsync()
    {
        var cauthStateProvder = (CustomAuthenticationStateProvider)authStateProvider;
        var user = await cauthStateProvder.GetAuthenticationStateAsync();
        if (user.User.Identity.IsAuthenticated)
        {
            mail = $"Welcome User # {user.User.Identity.Name}";
        }
    }
}