在Blazor中，我们可以使用Guard进行路由保护，防止已验证用户访问需要身份验证的页面。我们需要在启动文件中配置Guard，然后在需要保护的路由中使用AuthorizeRouteView组件。

以下是实现此目的的代码示例：

1. 在Startup.cs中配置Guard：

public void ConfigureServices(IServiceCollection services)
{
    services.AddAuthorizationCore();
    services.AddScoped();
    services.AddScoped();
    services.AddSingleton();
}

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseAuthentication();
    app.UseAuthorization();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
        endpoints.MapBlazorHub();
        endpoints.MapFallbackToPage("/_Host");
    });
}

在此示例中，我们在服务中添加了AuthorizationCore和CustomAuthorizationPolicyProvider，它们将用于自定义AuthorizationPolicy。接下来，我们在各自的Authorization Handler中添加了HasPermissionHandler和PermissionAuthorizationHandler。

2. 创建一个CustomAuthorizationPolicyProvider类：

public class CustomAuthorizationPolicyProvider : IAuthorizationPolicyProvider
{
    private readonly AuthorizationOptions _options;

    public CustomAuthorizationPolicyProvider(IOptions options)
    {
        _options = options.Value;
    }

    public Task GetPolicyAsync(string policyName)
    {
        foreach (var policy in _options.Policies)
        {
            if (policy.Name == policyName)
            {
                return Task.FromResult(policy);
            }
        }

        return Task.FromResult(null);
    }

    public Task GetDefaultPolicyAsync()
    {
        return Task.FromResult(new AuthorizationPolicyBuilder().RequireAuthenticatedUser().Build());
    }
}

此类指定默认策略为Authenticated User。

3. 添加HasPermissionHandler：

public class HasPermissionHandler : AuthorizationHandler
{
    protected override Task HandleRequirementAsync(AuthorizationHandlerContext context, HasPermissionRequirement requirement)
    {
        var permissionClaim = context