中间件类必须含有RequestDelegate 以及一个async 方法

namespace WebApplication1
{public class MiddleWare{private readonly RequestDelegate _requestDelegate;public MiddleWare(RequestDelegate requestDelegate){_requestDelegate = requestDelegate;}public async Task InvokeAsync(HttpContext context){string pwd = context.Request.Query["password"];if (pwd == "123")//假如路由中的querystring含有password且是123，则让继续访问{if (context.Request.HasJsonContentType()){context.Items["test"] = "123";}await _requestDelegate(context);//继续往下执行}else{context.Response.StatusCode = 401;}}}
}

注入

app.UseMiddleware<MiddleWare>();

https://www.tutorialsteacher.com/core/how-to-add-custom-middleware-aspnet-core