@inject SignInManager<IdentityUser> SignInManager
@inject UserManager<IdentityUser> UserManager

<ul class="navbar-nav">
    @if (SignInManager.IsSignedIn(User))
    {
        <li class="nav-item">
            <a class="nav-link" asp-area="Identity" asp-page="/Account/Manage/Index">Hello @User.Identity?.Name!</a>
        </li>
        <li class="nav-item">
            <form method="post" asp-area="Identity" asp-page="/Account/Logout">
                <button type="submit" class="nav-link btn btn-link">Logout</button>
            </form>
        </li>
    }
    else
    {
        <li class="nav-item">
            <a class="nav-link" asp-area="Identity" asp-page="/Account/Register">Register</a>
        </li>
        <li class="nav-item">
            <a class="nav-link" asp-area="Identity" asp-page="/Account/Login">Login</a>
        </li>
    }
</ul>