Example on how to use a POCO Settings class in ASP.NET Core

ClassLibrary\GoogleApiRequest.cs

public interface IGoogleApiRequest
{
  string ShowMyKey();
}

public class GoogleApiRequest : IGoogleApiRequest
{
  private readonly IGoogleApiSettings _settings;

  public GoogleApiRequest(IGoogleApiSettings settings) {
    if(settings == null) throw new ArgumentNullException(nameof(settings));
    _settings = settings;
  }
  
  public string ShowMyKey()
  {
    return $"Here's your key: {_settings.ApiKey}";
  }
}

ClassLibrary\GoogleApiSettings.cs

public interface IGoogleApiSettings
{
  string ApiKey { get; set; }
  
  bool EnablePlacesApi { get; set; }
}

public class GoogleApiSettings
{
  public string ApiKey { get; set; }
  
  public bool EnablePlacesApi { get; set; } = true;
}

WebApp\AddSecretCommand.bat

REM this is an example of how you add your secret
REM make sure you've reviewed the docs at http://docs.asp.net/en/latest/security/app-secrets.html
REM or at http://go.microsoft.com/fwlink/?LinkID=532709

user-secret set GoogleApiSettings:ApiKey YOUR-GOOGLE-API-KEY-HERE

WebApp\appsettings.json

{
	"AppSettings": {
    "SomeSetting": "???"
	},
	"GoogleApiSettings": {
		"ApiKey": "SINCE WE ARE USING USER SECRETS THIS SHOULD NEVER BE THE VALUE",
		"EnablePlacesApi": false
	},
	"Data": {
		"DefaultConnection": {
			"ConnectionString": "Server=localhost\\sqlexpress;Database=WebApp;Trusted_Connection=True;MultipleActiveResultSets=true"
		}
	}
}

WebApp\Controllers\HomeController.cs

public class HomeController : Controller {

	private IGoogleApiRequest _googleApiRequest;

	public HomeController(IGoogleApiRequest googleApiRequest)
	{
		_googleApiRequest = googleApiRequest;
	}

	// if you do constructor injection
	public IActionResult ApiKeyFromConstructor()
	{
		return Content(_googleApiRequest.ShowMyKey());
	}
      
	// if you do method body injection
	public IActionResult ApiKeyFromMethodBody([FromServices]IGoogleApiRequest fromServicesGoogleApiRequest)
	{
		return Content(fromServicesGoogleApiRequest.ShowMyKey());
	}
}

WebApp\project.json

// make sure to add this dependency:
"Microsoft.Extensions.Configuration.UserSecrets": "1.0.0-rc1-final",

WebApp\Startup.cs

using ClassLibrary;

// warning, incomplete class - provided for reference only

public partial class Startup
{
  public Startup()
  {
    // perform normal initialization from appsettings, etc
    
    // make sure to use this for user secrets
		if (hostingEnvironment.IsDevelopment())
		{
			builder.AddUserSecrets();
		}

		builder.AddEnvironmentVariables();
		Configuration = builder.Build();
  }


  public void ConfigureServices(IServiceCollection services)
  {
    // do other things
    
		var googleSettingsSection = Configuration.GetSection("GoogleApiSettings");

		// one way to do it - personally I prefer this over the IOptions API
		services.AddTransient<IGoogleApiSettings>(provider => googleSettingsSection.Get<GoogleApiSettings>());

		// or if you really want to make use of IOptions...
		services.AddOptions().Configure<GoogleApiSettings>(googleSettingsSection);
		// you can then override the construction of your injected service 
		services.AddTransient<IGoogleApiRequest>(
			provider =>
				{
					var options = provider.GetService<IOptions<GoogleApiSettings>>()?.Value;
					return new GoogleApiRequest(options);
				});
		
    // do more things
  }
}