在Asp.net Mvc中使用ReCaptcha

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Derik Whittaker » Using ReCaptcha with Asp.Net MVC

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Using ReCaptcha with Asp.Net MVC

For all the debate regarding if Captcha's are a good thing or a bad thing one thing is certain (in my book).  If you do not have some way to stop spam-bots your site will become overridden with junk in a hurry.

In an effort to reduce the amount of spam comments I am getting over at Dimecasts.net I finally got off my lazy ass and worked on implementing a Captcha.  The solution I ended up going with was reCaptcha.  I found that their setup was very easy to use and worked right out of the box.  However, there was not a lot of information on the net on how to use reCaptcha within an MVC site, only Asp.Net Webforms.  So I thought I would share my experiences and explain how I implemented reCaptcha on Dimecasts.

Step 1 - Signup for and download the reCaptcha dll from their site

Step 2 - Add reference to the Recaptcha.dll to your project

Step 3 - Create an Action Filter to handle the Captcha validation

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1. public class CaptchaValidatorAttribute : ActionFilterAttribute  
2. { 
3. private const string CHALLENGE_FIELD_KEY = "recaptcha_challenge_field"; 
4. private const string RESPONSE_FIELD_KEY = "recaptcha_response_field"; 
5. public override void OnActionExecuting(ActionExecutingContext filterContext) 
6.         { 
7.             var captchaChallengeValue = filterContext.HttpContext.Request.Form[CHALLENGE_FIELD_KEY]; 
8.             var captchaResponseValue = filterContext.HttpContext.Request.Form[RESPONSE_FIELD_KEY]; 
9.             var captchaValidtor = new Recaptcha.RecaptchaValidator 
10.                                       { 
11.                                           PrivateKey = -- PUT PRIVATE KEY HERE --, 
12.                                           RemoteIP = filterContext.HttpContext.Request.UserHostAddress, 
13.                                           Challenge = captchaChallengeValue, 
14.                                           Response = captchaResponseValue 
15.                                       }; 
16.             var recaptchaResponse = captchaValidtor.Validate(); 
17. // this will push the result value into a parameter in our Action
18.             filterContext.ActionParameters["captchaValid"] = recaptchaResponse.IsValid; 
19. base.OnActionExecuting(filterContext); 
20.         } 
21. } 

Step 4 - Implement the Controller Action that will handle the form submission and Captcha validation

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1. [CaptchaValidator] 
2. [AcceptVerbs( HttpVerbs.Post )] 
3. public ActionResult CreateComment( Int32 id, bool captchaValid ) 
4. { 
5. .. Do something here 
6. } 

Step 5 - Create a Html Helper to build and render the Captcha control

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1. public static string GenerateCaptcha( this HtmlHelper helper ) 
2. { 
3.     var captchaControl = new Recaptcha.RecaptchaControl 
4.             { 
5.                     ID = "recaptcha", 
6.                     Theme = "blackglass", 
7.                 PublicKey = -- Put Public Key Here --, 
8.                         PrivateKey = -- Put Private Key Here -- 
9.         }; 
10.     var htmlWriter = new HtmlTextWriter( new StringWriter() ); 
11.     captchaControl.RenderControl(htmlWriter); 
12. return htmlWriter.InnerWriter.ToString(); 
13. } 

Step 6 - Implement the logic in your view to actually render the Captcha control

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1. <:%= Html.GenerateCaptcha() %>: 

Step 7 - Oh wait, there is no step 7.  You are done.

There you go, that is all that is needed to setup reCaptcha for use in a MVC application

Till next time,

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