ASP.NET MVC Single Page Application CAPTCHA VB.NET Code Example

The ASP.NET MVC Single Page Application Captcha VB.NET example project shows the most basic source code required to protect an ASP.NET MVC form with BotDetect CAPTCHA and validate the user input.

First Time Here?

Check the BotDetect ASP.NET MVC Captcha Quickstart for key integration steps.

ASP.NET MVC View code displaying CAPTCHA protection can be found in Views/Account/Register.vbhtml, and the ASP.NET MVC Controller code checking user input is in Controllers/AccountController.vb.

Download the BotDetect ASP.NET CAPTCHA Generator archive to run this example

→ .NET programming language:

  • C#
  • VB.NET

Within this page, the root folder of the extracted archive is referred as the <BDC-DIR>.

This example is in the <BDC-DIR>/lgcy-on-lgcy/examples/t_api-captcha-mvc5-aspnet.identity-spa/vbnet/ folder; and contains the following files:


@ModelType RegisterViewModel
@* namespaces needed to access BotDetect members and the CaptchaHelper class *@
@Imports BotDetect.Web.Mvc
    ViewBag.Title = "Register"
End Code


@* include BotDetect layout stylesheet in page <head> *@
@Section HeadIncludes
    <link href="@BotDetect.Web.CaptchaUrls.Absolute.LayoutStyleSheetUrl" 
    rel="stylesheet" type="text/css" />
End Section

@Using Html.BeginForm("Register", "Account", FormMethod.Post, New With {.class = 
"form-horizontal", .role = "form"})


        <h4>Create a new account.</h4>
        <hr />
        <div class="col-md-6" id="form-container">
            @Html.ValidationSummary("", New With {.class = "text-danger"})
            <div class="form-group">
                @Html.LabelFor(Function(m) m.Email, New With {.class = "col-md-2 
                <div class="col-md-10">
                    @Html.TextBoxFor(Function(m) m.Email, New With {.class = 
            <div class="form-group">
                @Html.LabelFor(Function(m) m.Hometown, New With {.class = "col-
                md-2 control-label"})
                <div class="col-md-10">
                    @Html.TextBoxFor(Function(m) m.Hometown, New With {.class = 
            <div class="form-group">
                @Html.LabelFor(Function(m) m.Password, New With {.class = "col-
                md-2 control-label"})
                <div class="col-md-10">
                    @Html.PasswordFor(Function(m) m.Password, New With {.class = 
            <div class="form-group">
                @Html.LabelFor(Function(m) m.ConfirmPassword, New With {.class = 
                "col-md-2 control-label"})
                <div class="col-md-10">
                    @Html.PasswordFor(Function(m) m.ConfirmPassword, New With {.
                    class = "form-control"})
            @* showing Captcha on the form:
                add Captcha validation controls to the protected action View,
                but only if the Captcha hasn't already been solved *@

            @Code Dim registrationCaptcha As MvcCaptcha = CaptchaHelper.GetRegistrationCaptcha()
                If (Not registrationCaptcha.IsSolved) Then
                    @<div class="form-group">
                        <div class="col-md-offset-2 col-md-10">

                        @Html.Label("Retype the code", New With {.class = "col-
                        md-2 control-label"})

                        <div class="col-md-10">
                            @Html.TextBox("CaptchaCode", Nothing, New With {.
                            class = "form-control captchaVal"})
                End If
            End Code
            <div class="form-group">
                <div class="col-md-offset-2 col-md-10">
                    <input type="submit" class="btn btn-default" 
                    value="Register" />
                End Using

@section Scripts
End Section

To display Captcha protection on the example View, we first ensure we can use BotDetect members by Import-ing the relevant namespaces.

We then create a MvcCaptcha instance, and add it to the form by calling the Html.Captcha() Html helper with it.

In this simplest case, we also use the Html.ValidationMessage helper to display Captcha validation errors.


Imports System.Security.Claims
Imports System.Threading.Tasks
Imports Microsoft.AspNet.Identity
Imports Microsoft.AspNet.Identity.Owin
Imports Microsoft.Owin.Security
Imports BotDetect.Web.Mvc

Public Class AccountController
    Inherits Controller
    Private _signInManager As ApplicationSignInManager
    Private _userManager As ApplicationUserManager

    Public Sub New()
    End Sub

    Public Sub New(appUserMan As ApplicationUserManager, signInMan As 
        UserManager = appUserMan
        SignInManager = signInMan
    End Sub


    ' GET: /Account/Register
    Public Function Register() As ActionResult
        Return View()
    End Function

    ' POST: /Account/Register
    <CaptchaValidationActionFilter("CaptchaCode", "RegistrationCaptcha", "Incorrect CAPTCHA Code!")>
    Public Async Function Register(model As RegisterViewModel) As Task(Of 
        If ModelState.IsValid Then
            Dim user = New ApplicationUser() With {
                .UserName = model.Email,
                .Email = model.Email,
                .Hometown = model.Hometown
            Dim result = Await UserManager.CreateAsync(user, model.Password)
            If result.Succeeded Then
                Await SignInManager.SignInAsync(user, isPersistent:=False, 

                ' For more information on how to enable account confirmation and 
                password reset please visit
                ' Send an email with this link
                ' Dim code = Await UserManager.
                ' Dim callbackUrl = Url.Action("ConfirmEmail", "Account", New 
                With { .userId = user.Id, .code = code }, protocol := Request.
                ' Await UserManager.SendEmailAsync(user.Id, "Confirm your 
                account", "Please confirm your account by clicking <a href=""" & 
                callbackUrl & """>here</a>")
                Return RedirectToAction("Index", "Home")
            End If
        End If

        ' If we got this far, something failed, redisplay form
        Return View(model)
    End Function

End Class

After we've included the BotDetect.Web.Mvc namespace, we just need to add the CaptchaValidationActionFilter attribute to the method processing form submissions. The attribute takes three parameters:

  1. the ID of the textbox containing the user's Captcha code input (which we named CaptchaCode on the form),
  2. the ID of the Captcha instance we're validating (which we set to ExampleCaptcha in the MvcCaptcha constructor), and
  3. the error message to be shown when Captcha validation fails.

When the Captcha validation action filter attribute has been added, the Captcha validation will trigger every time the form is submitted, and will automatically add a Model error with the error message configured above when Captcha validation fails. The Html.ValidationMessage helper on the form will then display this error when Captcha validation fails.


Imports System
Imports System.Collections.Generic
Imports System.Linq
Imports System.Web
Imports System.Web.Mvc
Imports System.Web.Routing

Public Module RouteConfig
  Public Sub RegisterRoutes(ByVal routes As RouteCollection)

    ' BotDetect requests must not be routed
    New With {.botdetect = "(.*)BotDetectCaptcha\.ashx"})

    routes.MapRoute( _
        name:="Default", _
        url:="{controller}/{action}/{id}", _
        defaults:=New With {.controller = "Example", .action = "Index", .
        id = UrlParameter.Optional} _
  End Sub
End Module

We configure ASP.NET Routing to ignore BotDetect requests, since they do not conform to any MVC-related patterns. The regex defining requests to ignore must match the path configured for the BotDetect HttpHandler registered in web.config.


<?xml version="1.0" encoding="utf-8"?>
  For more information on how to configure your ASP.NET application, please 
    <!-- For more information on Entity Framework configuration, visit http://go. -->
    <section name="botDetect" requirePermission="false" 
    type="BotDetect.Configuration.BotDetectConfigurationSection, BotDetect"/>
    <add name="DefaultConnection" connectionString="Data Source=(LocalDb)
    mdf;Initial Catalog=aspnet-CSharp-20150616040032;Integrated Security=True"
      providerName="System.Data.SqlClient" />

    <add key="webpages:Version" value="" />
    <add key="webpages:Enabled" value="false" />
    <add key="ClientValidationEnabled" value="true" />
    <add key="UnobtrusiveJavaScriptEnabled" value="true" />
    <authentication mode="None" />
    <compilation debug="true" targetFramework="4.6" />
    <httpRuntime targetFramework="4.6" />
    <!-- configure Session State for BotDetect use -->
    <sessionState mode="InProc" cookieless="AutoDetect" timeout="20" 
    sessionIDManagerType="BotDetect.Web.CustomSessionIdManager, BotDetect"/>
      <!-- register HttpHandler used for BotDetect Captcha requests -->
      <add verb="GET" path="BotDetectCaptcha.ashx" 
      type="BotDetect.Web.CaptchaHandler, BotDetect"/>
    <validation validateIntegratedModeConfiguration="false"/>
      <remove name="FormsAuthentication" />
      <!-- Register the HttpHandler used for BotDetect Captcha requests (IIS 7.0+) -->
      <remove name="BotDetectCaptchaHandler"/>
      <add name="BotDetectCaptchaHandler" preCondition="integratedMode"
      verb="GET" path="BotDetectCaptcha.ashx" 
      type="BotDetect.Web.CaptchaHandler, BotDetect"/>
      <remove name="ExtensionlessUrlHandler-Integrated-4.0" />
      <remove name="OPTIONSVerbHandler" />
      <remove name="TRACEVerbHandler" />
      <add name="ExtensionlessUrlHandler-Integrated-4.0" path="*." verb="*" 
      preCondition="integratedMode,runtimeVersionv4.0" />
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
        <assemblyIdentity name="Microsoft.Owin" 
        publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="" newVersion="" />
        <assemblyIdentity name="Microsoft.Owin.Security.OAuth" 
        publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="" newVersion="" />
        <assemblyIdentity name="Microsoft.Owin.Security.Cookies" 
        publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="" newVersion="" />
        <assemblyIdentity name="Microsoft.Owin.Security" 
        publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="" newVersion="" />
        <assemblyIdentity name="Newtonsoft.Json" culture="neutral" 
        publicKeyToken="30ad4fe6b2a6aeed" />
        <bindingRedirect oldVersion="" newVersion="" />
        <assemblyIdentity name="System.Web.Optimization" 
        publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="" newVersion="" />
        <assemblyIdentity name="WebGrease" publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="" newVersion="1.5.2.
        14234" />
        <assemblyIdentity name="System.Web.Helpers" 
        publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="" newVersion="" />
        <assemblyIdentity name="System.Web.WebPages" 
        publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="" newVersion="" />
        <assemblyIdentity name="System.Web.Mvc" 
        publicKeyToken="31bf3856ad364e35" />
        <bindingRedirect oldVersion="" newVersion="" />
  <botDetect helpLinkEnabled="true" helpLinkMode="image" />

To allow the application to use BotDetect Captcha protection, we must register the BotDetect HttpHandler in both <system.web><httpHandlers> and <system.webServer><handlers> configuration sections, and enable and configure ASP.NET sessionState.

The <dependentAssembly> entry for System.Web.Mvc is also needed to make all ASP.NET MVC dependencies referenced by the BotDetect MVC assembly point to the correct ASP.NET MVC version.