When to use Map and MapWhen branch in asp.net core middleware while we are authenticating request.

```cs
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    app.Map("", (appBuilder) =>
    {
        appBuilder.Run(async (context) => {
            await context.Response.WriteAsync("");
        });
    });

    app.MapWhen(context => context.Request.Query.ContainsKey(""), (appBuilder) =>
    {
        appBuilder.Run(async (context) =>
        {
            await context.Response.WriteAsync("");
        });

    });
}

```