Sure, I can provide you with a simple example of implementing a CAPTCHA in an MVC 5 (Model-View-Controller) application using C#. In this example, we'll use the NuGet package "SimpleCaptcha" to generate the CAPTCHA.
Step 1: Create a new MVC 5 Project
Start by creating a new MVC 5 project in Visual Studio.
Step 2: Install SimpleCaptcha Package
Right-click on your project in the Solution Explorer, select "Manage NuGet Packages," search for "SimpleCaptcha," and install the package.
Step 3: Create a CAPTCHA Controller
Create a new controller named "CaptchaController" by right-clicking on the "Controllers" folder and selecting "Add" > "Controller." Name the controller "CaptchaController."
Step 4: Generate a CAPTCHA Image
Inside the "CaptchaController," create an action method that generates a CAPTCHA image and stores the CAPTCHA value in the session for validation later.
```csharp
using System.Web.Mvc;
using SimpleCaptcha;
public class CaptchaController : Controller
{
public ActionResult Index()
{
// Generate a new CAPTCHA image
var captcha = new SimpleCaptchaImage();
var captchaImage = captcha.GetImage(100, 50, 6, true);
// Store the CAPTCHA value in the session for validation
Session["CaptchaCode"] = captcha.CaptchaCode;
// Return the CAPTCHA image as a FileResult
return File(captchaImage, "image/png");
}
}
```
Step 5: Create a View to Display CAPTCHA Image
Create a new view named "Index.cshtml" inside the "Views/Captcha" folder. Add the following code to the view to display the CAPTCHA image.
```html
@{
Layout = null;
}
CAPTCHA Example
@Html.TextBox("CaptchaInput", "", new { placeholder = "Enter CAPTCHA code" })
```
Step 6: Validate CAPTCHA Input
Back in the "CaptchaController," create another action method to validate the user's input against the CAPTCHA value stored in the session.
```csharp
public class CaptchaController : Controller
{
// ... (previous code)
[HttpPost]
public ActionResult Validate(string captchaInput)
{
// Get the stored CAPTCHA value from the session
var storedCaptcha = Session["CaptchaCode"] as string;
if (string.IsNullOrEmpty(storedCaptcha) || string.IsNullOrEmpty(captchaInput))
{
// CAPTCHA validation failed
return View("Error");
}
// Convert both the CAPTCHA values to lowercase for case-insensitive comparison
if (storedCaptcha.ToLower() == captchaInput.ToLower())
{
// CAPTCHA validation successful
return View("Success");
}
else
{
// CAPTCHA validation failed
return View("Error");
}
}
}
```
Step 7: Create Success and Error Views
Create two views named "Success.cshtml" and "Error.cshtml" inside the "Views/Captcha" folder to display a success or error message when the CAPTCHA validation is complete.
"Success.cshtml":
```html
@{
Layout = null;
}
CAPTCHA Validation Successful
Thank you for completing the CAPTCHA successfully.
```
"Error.cshtml":
```html
@{
Layout = null;
}
CAPTCHA Validation Failed
Sorry, the CAPTCHA code you entered is incorrect. Please try again.
```
Step 8: Update RouteConfig
Finally, update the "RouteConfig.cs" file (located in the "App_Start" folder) to add a custom route for the CAPTCHA image.
```csharp
public class RouteConfig
{
public static void RegisterRoutes(RouteCollection routes)
{
routes.IgnoreRoute("{resource}.axd/{pathInfo}");
// Add the custom route for the CAPTCHA image
routes.MapRoute(
name: "CaptchaImage",
url: "Captcha/Index",
defaults: new { controller = "Captcha", action = "Index" }
);
routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);
}
}
```
Now, when you navigate to the "/Captcha" route, you will see a CAPTCHA image. When users submit their CAPTCHA input, they will be redirected to either the "Success" or "Error" view based on the validation result.
Please note that this is a basic example for educational purposes. In a real-world scenario, you might want to implement additional security measures, like rate-limiting and enforcing the CAPTCHA only for specific actions.