Blazor Server Side应用程序使用SignalR与服务器进行通信，因此可以使用SignalR的相关事件来实现用户在关闭选项卡或浏览器时自动注销。

1. 在Startup.cs文件中添加以下代码来配置SignalR:

 services.AddSignalR();

2. 在App.razor文件中添加以下代码来注册SignalR的事件:

@inject NavigationManager NavigationManager
@inject IJSRuntime JSRuntime

@implements IDisposable

private HubConnection hubConnection;
private string connectionErrorMessage;

protected async override Task OnInitializedAsync()
{
    hubConnection = new HubConnectionBuilder()
        .WithUrl(NavigationManager.ToAbsoluteUri("/myHub"))
        .Build();

    hubConnection.On("Logout", (message) =>
    {
        JSRuntime.InvokeVoidAsync("alert", message);
        NavigationManager.NavigateTo("/");
    });

    try
    {
        await hubConnection.StartAsync();
    }
    catch (Exception ex)
    {
        connectionErrorMessage = ex.Message;
    }
}

public async ValueTask DisposeAsync()
{
    if (hubConnection != null)
    {
        await hubConnection.DisposeAsync();
    }
}

3. 在Server项目中创建一个Hub类，并添加以下代码:

public class MyHub : Hub
{
    public async Task LogoutAsync(string message)
    {
        await Clients.All.SendAsync("Logout", message);
    }

    public override async Task OnDisconnectedAsync(Exception exception)
    {
        await LogoutAsync("用户已注销");
        await base.OnDisconnectedAsync(exception);
    }
}

4. 修改Logout页面的代码，添加以下代码:

@inject NavigationManager NavigationManager
@inject HubConnection hubConnection

@page "/logout"

@if (hubConnection.State == HubConnectionState.Disconnected)
{
    
@("SignalR连接错误：" + hubConnection.GetConnectionErrorMessage())
}
else
{
    
正在注销...
}

@code {
    protected override async Task OnInitializedAsync()
    {
        await hubConnection.SendAsync("LogoutAsync", "用户已注销");
        NavigationManager.NavigateTo("/", force