在 Blazor WebAssembly 应用程序中将 JWT 放在请求头部的解决方法如下所示：

1. 创建一个名为 JwtInterceptor.cs 的新类，用于拦截每个请求，并在请求头部添加 JWT。

using System.Net.Http;
using System.Net.Http.Headers;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Components;
using Microsoft.AspNetCore.Components.WebAssembly.Hosting;

public class JwtInterceptor : DelegatingHandler
{
    private readonly NavigationManager _navigationManager;

    public JwtInterceptor(NavigationManager navigationManager)
    {
        _navigationManager = navigationManager;
    }

    protected override async Task SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        var token = await GetTokenAsync();
        
        if (!string.IsNullOrEmpty(token))
        {
            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", token);
        }

        return await base.SendAsync(request, cancellationToken);
    }

    private async Task GetTokenAsync()
    {
        // 从 localStorage 或其他地方获取 JWT Token
        var token = await // 获取 Token 的逻辑

        return token;
    }
}

2. 在 Program.cs 中注册 JwtInterceptor 类作为 HttpClient 的拦截器。

using Microsoft.AspNetCore.Components.WebAssembly.Hosting;
using Microsoft.Extensions.DependencyInjection;

public class Program
{
    public static async Task Main(string[] args)
    {
        var builder = WebAssemblyHostBuilder.CreateDefault(args);
        builder.RootComponents.Add("app");

        // 注册 JwtInterceptor 类
        builder.Services.AddScoped();

        // 注册 HttpClient，并设置其拦截器为 JwtInterceptor
        builder.Services.AddScoped(sp => new HttpClient { BaseAddress = new Uri(builder.HostEnvironment.BaseAddress) }
            .AddHttpMessageHandler());

        await builder.Build().RunAsync();
    }
}

通过上述代码，每次发送 HTTP 请求时，JwtInterceptor 类都会拦截请求并在请求头部添加 JWT。