In Memory Configuration Provider Sample

Program.cs

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

    public static IHostBuilder CreateHostBuilder(string[] args)
    {
        // Populate the configuration settings somehow   
        // E.g. hard-coding or loading from other source.
        var inMemoryConfigSettings = new Dictionary<string, string>()
        {
            { "Mode", "MemoryConfigProvider" },
            { "MailFeature:0:Subject", "Dev Subject Marketing" },
            { "MailFeature:1:Subject", "Dev Subject Users" },
            { "MailFeature:2:Subject", "Dev Subject Orders" },
            { "Logging:LogLevel:Default", "Error" }
        };

        // AddInMemoryCollection to load these settings as key-value pairs
        // so that they can be available via IConfiguration instance.
        return Host.CreateDefaultBuilder(args)
            .ConfigureAppConfiguration((hostingContext, config) =>
            {
                config.AddInMemoryCollection(inMemoryConfigSettings);
            })
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });
    }
}