Can you tell me how I can do that? And how the urls would be?

您可以在解决方案中拥有’n’个项目.您需要使用RouteConfig.cs处理它,如果您有三个项目,如’Project1′,’Project2’和’Project3′.然后您的相应路由配置将如下所示：

routes.MapRoute(
    name: "Default_1",url: "Project1/{controller}/{action}/{id}",defaults: new { controller = "Home",action = "Index",id = UrlParameter.Optional }
);

同样的,

routes.MapRoute(
    name: "Default_2",url: "Project2/{controller}/{action}/{id}",id = UrlParameter.Optional }
);

Is it possible for a user to be logged in in all projects when he
logs in once?

是的,这绝对是可能的.但开箱即用的ASP.NET身份不支持多个应用程序.有人说通过Single Sign On实现它是开发人员的任务

链接：How to implement it

希望能帮助到你！