Configuration providers
A configuration provider is an implementation of IConfigurationProvider that is created by a configuration source, which is an implementation of IConfigurationSource. The configuration provider then reads the data from somewhere and provides it via Dictionary.
To add a custom or third-party configuration provider to ASP.NET Core, you will need to call the Add method on ConfigurationBuilder and insert the configuration source. This is just an example:
Host.CreateDefaultBuilder(args)
    .ConfigureWebHostDefaults(webBuilder =>
    {
       Â
       webBuilder.ConfigureAppConfiguration((builderContext,
         config) =>
        {
            var env = builderContext.HostingEnvironment;
            config.SetBasePath(env.ContentRootPath);
            config.AddJsonFile(
                "appsettings.json",
                optional: false,
                reloadOnChange: true);
            config.AddJsonFile(
                $"appsettings.{env.EnvironmentName}.json",
                optional: true,
                reloadOnChange: true);
            // add new configuration source
            config.Add(new MyCustomConfigurationSource
            {
                SourceConfig = //configure whatever source
                Optional = false,
                ReloadOnChange = true
            });
            config.AddEnvironmentVariables();
        })
        .UseStartup<Startup>();
    });
Usually, you would create an extension method to add the configuration source more easily:
config.AddMyCustomSource("source", optional: false,
     reloadOnChange: true);
A really detailed concrete example about how to create a custom configuration provider has been written by Andrew Lock. You can find this in the Further reading section of this chapter.
