ReCaptcha Web Helper in ASP.NET MVC 3 RC

ASP.NET MVC 3 RC contains a full suite of web helpers that Microsoft have made available through the Microsoft Web Helpers library. This can be downloaded through NuGet (formerly NuPack). NuGet is a free open source package manager that makes it easy for you to find, install, and use .NET libraries in your projects. One web helpers that is long overdue is the ReCaptcha web helper. Captcha is a type of challenge-response test used in computing to ensure that the response is not generated by a computer. This article will show you how to download the library and start using this web helper. This code also works in WebMatrix if you're using it.

Before moving on, you need to download ASP.NET MVC 3 RC. Click here to download and install them using the Microsoft Web Platform Installer.

Open studio 2010 and create a new ASP.NET MVC 3 Web Application (Razor) project. The new MVC 3 dialog can be seen below:

Choose Razor as the view engine and click OK.

The next step is to download the Microsoft Web Helpers library through NuGet. Follow these steps to do this:

Step 1: Right click the website and choose Add Package Reference.

Step 2: The Add Package Reference dialog will open. Search for Microsoft in the search box in the top right corner. Upon completion you'll see microsoft-web-helpers option. Select that option and click Install.

Step 3: Click Close to return to the project

Check the references and you'll see that the library has been added to the project.

Now it's time to start coding! The web helper I’m focusing on today is the ReCaptcha web helper. This web helper renders a captcha control in your form so you can validate that this, to the best of your knowledge, a human submitting the form. The code below demonstrates how to include the ReCaptcha web helper:

@ReCaptcha.GetHtml(theme: "red")

All of the GetHtml parameters are optional. You can use the new optional parameters in C# 4.0 to pass all or single parameters. The list below outlines the parameters:

• theme – the theme that will be used by the website
• language – the language to display the captcha challenge
• tabIndex – the tab index of this control
• publicKey – a unique identifier for your domain

The following screen-shot demonstrates how to use the ReCaptcha web helper: 



Before moving on you must generate a public and private key. This is outside the bounds of this article, but it’s a unique identifier for your domain. You can go here to generate these keys. Once the keys have been generated, you must add the public key to the ReCaptcha web helper that will be rendered in the browser. The private key will be used in the server side code to verify the incoming captcha request. I’m adding the public key value to the _ViewStart page. _ViewStart is a page that will be executed before any view is rendered. This ensures that whatever common code I put in there will be available to all the views. Add a new page to the Views folder and call it _ViewStart.cshtml. Add the following code: 



The public key in this article is for demonstration purposes only. To validate the user has entered the correct value when submitting the form, you will use the ReCaptcha.Validate method. The following code demonstrates how to validate the ReCaptcha code in an action method: 



You must pass the private key to the ReCaptcha.Validate method. This will ensure the validation between the client and server are correct. If you build the application now and enter in the incorrect captcha, you'll see a Failed message returned, otherwise it'll be Ok.

The ReCaptcha web helper is a welcome addition to the framework. It certainly takes the pain out of adding captcha controls/widgets to your website.

The entire source code of this article can be downloaded over here

This article has been editorially reviewed by Suprotim Agarwal.

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Author

Malcolm Sheridan is a Microsoft awarded MVP in ASP.NET, a Telerik Insider and a regular presenter at conferences and user groups throughout Australia and New Zealand. Being an ASP.NET guy, his focus is on web technologies and has been for the past 10 years. He loves working with ASP.NET MVC these days and also loves getting his hands dirty with jQuery and JavaScript. He also writes technical articles on ASP.NET for SitePoint and other various websites. Follow him on twitter @malcolmsheridan