StartupConfigureInLineGist.cs

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

    app.Use(async (context, next) =>
    {
        var userAgent = context.Request.Headers.GetCommaSeparatedValues("User-Agent").LastOrDefault();

        if (userAgent is not null)
        {
            // Note that as ILogger<T> requres a type, we have to use Startup 
            // here which doesn't really seem right!
            var logger = app.ApplicationServices.GetRequiredService<ILogger<Startup>>();
            logger?.LogTrace($"User Agent : {userAgent}");
        }
        await next();
    });

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
    });
}