title: Access IConfiguration in the ActionFilterAttribute in the asp.net core rc2 application
body: <p>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:</p>
  
  <pre><code>public ValidateReCaptchaAttribute(IConfiguration configuration)
          {
              if (configuration == null)
              {
                  throw new ArgumentNullException("configuration");
              }
  
              this.m_configuration = configuration;
          }
  </code></pre>
  
  <p>because when I decorate method with <code>[ValidateReCaptcha]</code> I can't pass config</p>
  
  <p>So how do I can read something from config from the method in attribute class?</p>