.Net Core 3.1 adding additional config.json file to configuration argument in Startup

Question

I need to add another configuration file to my .Net Core Blazor project. Other sources (such as this) mention using configuration builder in .Net core 2.2, but since in 3.1 the configuration is passed in as a parameter into Startup, I have no way of appending another config onto it- as far as I can tell at least. Maybe I'm looking at it wrong, but I'm assuming that the configuration passed in as a param has important configuration properties, therefor building it myself with just the additional config file seems like it leaves those config properties out.

Ex: Doesn't work but should paint a picture of what I'm trying to do.

public Startup(IConfiguration configuration)
{
      Configuration = configuration;
      var builder = new ConfigurationBuilder(configuration)
              .AddJsonFile("accountconstants.json", optional: true, reloadOnChange: true);
      });
}

*Edit from the future: Typos.

Answer 1

You can do it in Program.cs i.e. earlier in the pipeline rather than in Startup.cs.

Example:

public class Program
{
    public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureAppConfiguration((hostContext, config) =>
            {
                var env = hostContext.HostingEnvironment;

                config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
                    .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);
            })
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
}