TestController.cs

public class TestController : Controller
{
  private IConfiguration _configuration;
  
  public TestController(IConfiguration configuration)
  {
    _configuration = configuration;
    Debug.WriteLine($"Config (MyKey): {_configuration.GetSection("MyKey")}");
    Debug.WriteLine($"Config (App:Name): {_configuration.GetSection("App:Name")}");
    Debug.WriteLine($"Config (App:Organisation:Email): {_configuration.GetSection("App:Organisation:Email")}");
  }
  
  ...
}