通过 SignInManager 展示登录状态

通过注入 SignInManager 完成登录状态的显式：

<div class="container">
    @inject SignInManager<IdentityUser> SignInManager
    <nav class="navbar navbar-expand-sm bg-dark navbar-dark">
        ...
        <div class="collapse navbar-collapse" id="collapsibleNavbar">
            ...
            <ul class="navbar-nav ml-auto">
                @if (SignInManager.IsSignedIn(User))
                {
                    <li class="nav-item">
                        <form asp-controller="Account" asp-action="Logout" method="post">
                            <button type="submit" style="width: auto" class="nav-link btn btn-link py-0">
                                注销 @User.Identity.Name
                            </button>
                        </form>
                    </li>
                }
                else
                {
                    <li class="nav-item">
                        <a class="nav-link" asp-controller="Account" asp-action="Register">注册</a>
                    </li>
                    <li class="nav-item">
                        <a class="nav-link" asp-controller="Account" asp-action="Login">登录</a>
                    </li>
                }
            </ul>
        </div>
    </nav>
    @RenderBody()
</div>

注销

[HttpPost]
public async Task<IActionResult> Logout()
{
    await _signInManager.SignOutAsync();
    return RedirectToAction("Index", "Home");
}