Access IConfiguration in the ActionFilterAttribute in the asp.net core rc2 application [duplicate]

Question

I am writing attribute that will verify captcha. In order to work correctly it needs to know secret, which I keep in the settings (Secret manager tool). However I don't know how to read config from the attribute class. DI in asp.net core supports constructor injection (and property injection is not supported), so this will give compilation error:

public ValidateReCaptchaAttribute(IConfiguration configuration)
        {
            if (configuration == null)
            {
                throw new ArgumentNullException("configuration");
            }

            this.m_configuration = configuration;
        }

because when I decorate method with [ValidateReCaptcha] I can't pass config

So how do I can read something from config from the method in attribute class?

Answer 1

You can use ServiceFilter attribute, more info in this blog post and asp.net docs.

[ServiceFilter(typeof(ValidateReCaptchaAttribute))]
public IActionResult SomeAction()

In Startup

public void ConfigureServices(IServiceCollection services)
{
       // Add functionality to inject IOptions<T>
       services.AddOptions();

       // Add our Config object so it can be injected
       services.Configure<CaptchaSettings>(Configuration.GetSection("CaptchaSettings"));

       services.AddScoped<ValidateReCaptchaAttribute>();
       ...
}

And ValidateReCaptchaAttribute

public class ValidateReCaptchaAttribute : ActionFilterAttribute
{
     private readonly CaptchaSettings _settings;

     public ValidateReCaptchaAttribute(IOptions<CaptchaSettings> options)
     {
         _settings = options.Value;
     }

     public override void OnActionExecuting(ActionExecutingContext context)
     {
         ...
         base.OnActionExecuting(context);
     }
}

Answer 2

You should use ServiceFilter like this:

[ServiceFilter(typeof(ValidateReCaptcha))]

And if you want to use IConfiguration you should inject it in ConfigureServices:

services.AddSingleton((provider)=>
{
     return Configuration;
});