GoogleReCaptcha.V3

Library for Google's ReCaptcha v3 backend https://www.google.com/recaptcha

Target platform: .NET Core 3.1+

When targeting Core 3.0 use package version 1.1.2

Interface

Task<bool> IsCaptchaPassedAsync(string token);
Task<JObject> GetCaptchaResultDataAsync(string token);
void UpdateSecretKey(string key);

Setup guide

Install the package https://www.nuget.org/packages/GoogleReCaptcha.V3/ using nuget Update your appsetting.json config file

"googleReCaptcha:SiteKey": "YOUR_SITE_KEY",
"googleReCaptcha:SecretKey": "YOUR_SECRET_KEY"
"googleReCaptcha:MinimumScore": "YOUR_MINIMUM_ACCEPTABLE_SCORE"

You can get your keys here: https://www.google.com/recaptcha/admin

Update your middleware

services.AddHttpClient<ICaptchaValidator, GoogleReCaptchaValidator>();

Update your Views

@inject Microsoft.Extensions.Configuration.IConfiguration Configuration

<form asp-action="FormPost">
    <input type="hidden" name="captcha" id="captchaInput" value=""/>
    ...
</form>

@section Scripts
{
    <script src="https://www.google.com/recaptcha/api.js?render=@Configuration["googleReCaptcha:SiteKey"]"></script>
    <script>
    grecaptcha.ready(function() {
        grecaptcha.execute('@Configuration["googleReCaptcha:SiteKey"]', { action: 'contact' }).then(function (token) {
            $("#captchaInput").val(token);
        });
    });
    </script>
}

Update your controller

inject ICaptchaValidator

public class HomeController : Controller
{
  private readonly ICaptchaValidator _captchaValidator;
  public HomeController(ICaptchaValidator captchaValidator)
  {
      _captchaValidator = captchaValidator;
  }
  [HttpPost]
  public async Task<IActionResult> FormPost(Model collection, string captcha){
    if (!await _captchaValidator.IsCaptchaPassedAsync(captcha))
    {
        ModelState.AddModelError("captcha","Captcha validation failed");
    }
    if(ModelState.IsValid){
        ...
    }
    return View(collection)
  }

Additional info

You can use following method instead to get all response data

async Task<JObject> GetCaptchaResultDataAsync(string token)

To update secret key there is method.

void UpdateSecretKey(string key);

Method must be called jsut before the validation await _captchaValidator.IsCaptchaPassedAsync(captcha) after the form has been sent like this:

[HttpPost]
public async Task<IActionResult> Register(SampleViewModel collection, string captcha)
{
    _captchaValidator.UpdateSecretKey("NEW SECRET KEY");
    if (!await _captchaValidator.IsCaptchaPassedAsync(captcha))
    {
        ModelState.AddModelError("captcha","Captcha validation failed");
    }
    if(ModelState.IsValid)
    {
        ViewData["Message"] = "Success";
    }
    return View(collection);
}

Exceptions

Methods can throw 'HttpRequestException' when connection to the Google's service doesn't work or service doesn't response with HTTP 200

Contact

Contact me in case you find any errors or problem via email [email protected]