Blazor WASM：已认证用户禁止访问登录路由的实现方案

方案一：在Login组件内直接判断跳转 #

这是最直接的实现方式，在登录页面初始化时检查用户认证状态，若已认证则直接跳转到首页或指定页面。

@page "/login"
@inject AuthenticationStateProvider AuthStateProvider
@inject NavigationManager NavManager

protected override async Task OnInitializedAsync()
{
    var authState = await AuthStateProvider.GetAuthenticationStateAsync();
    if (authState.User.Identity?.IsAuthenticated == true)
    {
        // 跳转到首页，可根据业务需求修改目标路由
        NavManager.NavigateTo("/", forceLoad: false);
    }
}

<!-- 此处保留原有的登录UI代码 -->

方案二：全局导航拦截 #

通过监听导航事件，在用户跳转时全局判断目标路由与认证状态，实现统一拦截。可以在MainLayout中实现：

@inject AuthenticationStateProvider AuthStateProvider
@inject NavigationManager NavManager
@implements IDisposable

@code {
    protected override void OnInitialized()
    {
        NavManager.LocationChanged += OnLocationChanged;
    }

    private async void OnLocationChanged(object sender, LocationChangedEventArgs e)
    {
        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
        var targetPath = NavManager.ToBaseRelativePath(e.Location);
        
        // 拦截已认证用户访问/login路由
        if (targetPath.Equals("login", StringComparison.OrdinalIgnoreCase) 
            && authState.User.Identity?.IsAuthenticated == true)
        {
            // replace: true 会替换浏览器历史记录，避免用户回退到登录页
            NavManager.NavigateTo("/", replace: true);
        }
    }

    public void Dispose()
    {
        NavManager.LocationChanged -= OnLocationChanged;
    }
}

方案三：自定义RouteView实现路由守卫 #

这种方式更符合Blazor的组件化设计思想，通过替换默认的RouteView，实现路由级别的认证拦截：

1. 创建自定义RouteView类：

using Microsoft.AspNetCore.Components;
using Microsoft.AspNetCore.Components.Authorization;
using Microsoft.AspNetCore.Components.Routing;

public class CustomRouteView : RouteView
{
    [Inject]
    public AuthenticationStateProvider AuthStateProvider { get; set; } = default!;

    [Inject]
    public NavigationManager NavManager { get; set; } = default!;

    protected override async Task RenderAsync(RenderTreeBuilder builder)
    {
        var authState = await AuthStateProvider.GetAuthenticationStateAsync();
        var isAuthenticated = authState.User.Identity?.IsAuthenticated == true;
        var targetRoute = NavManager.ToBaseRelativePath(NavManager.Uri);

        // 拦截已认证用户访问login路由
        if (targetRoute.Equals("login", StringComparison.OrdinalIgnoreCase) && isAuthenticated)
        {
            NavManager.NavigateTo("/", replace: true);
            return;
        }

        // 正常渲染路由组件
        await base.RenderAsync(builder);
    }
}

2. 在App.razor中替换默认的RouteView：

<Router AppAssembly="@typeof(App).Assembly">
    <Found Context="routeData">
        <CustomRouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)" />
    </Found>
    <NotFound>
        <LayoutView Layout="@typeof(MainLayout)">
            <p>抱歉，该地址不存在。</p>
        </LayoutView>
    </NotFound>
</Router>

内容的提问来源于stack exchange，提问作者developer_009