How to authenticate against the Active Directory by using forms authentication and Visual Basic .NET

Create an ASP.NET Web Application in Visual Basic .NET

1. Start Microsoft Visual Studio .NET.
2. On the File menu, point to New, and then click Project.
3. Click Visual Basic Projects under Project Types, and then click ASP.NET Web Application under Templates.
4. In the Location box, type http://<servername>/FormsAuthAd (Replacing http://localhost if you are using the local server (so as to have http://localhost/FormsAuthAd, and then click OK.
5. Right-click the References node in Solution Explorer, and then click Add Reference.
6. On the .NET tab in the Add Reference dialog box, click System.DirectoryServices.dll, click Select, and then click OK.

Write the Authentication Code

1. In Solution Explorer, right-click the project node, point to Add, and then click Add New Item.
2. Click Class under Templates.
3. Type LdapAuthentication.vb in the Name box, and then click Open.
4. Replace the existing code in the LdapAuthentication.vb file with the following code:

   Imports System
   Imports System.Text
   Imports System.Collections
   Imports System.DirectoryServices
   
   Namespace FormsAuth
       Public Class LdapAuthentication
   
           Dim _path As String
           Dim _filterAttribute As String
   
           Public Sub New(ByVal path As String)
               _path = path
           End Sub
   
           Public Function IsAuthenticated(ByVal domain As String, ByVal username As String, ByVal pwd As String) As Boolean
   
               Dim domainAndUsername As String = domain & "\" & username
               Dim entry As DirectoryEntry = New DirectoryEntry(_path, domainAndUsername, pwd)
   
               Try
                   'Bind to the native AdsObject to force authentication.			
                   Dim obj As Object = entry.NativeObject
                   Dim search As DirectorySearcher = New DirectorySearcher(entry)
   
                   search.Filter = "(SAMAccountName=" & username & ")"
                   search.PropertiesToLoad.Add("cn")
                   Dim result As SearchResult = search.FindOne()
   
                   If (result Is Nothing) Then
                       Return False
                   End If
   
                   'Update the new path to the user in the directory.
                   _path = result.Path
                   _filterAttribute = CType(result.Properties("cn")(0), String)
   
               Catch ex As Exception
                   Throw New Exception("Error authenticating user. " & ex.Message)
               End Try
   
               Return True
           End Function
   
           Public Function GetGroups() As String
               Dim search As DirectorySearcher = New DirectorySearcher(_path)
               search.Filter = "(cn=" & _filterAttribute & ")"
               search.PropertiesToLoad.Add("memberOf")
               Dim groupNames As StringBuilder = New StringBuilder()
   
               Try
                   Dim result As SearchResult = search.FindOne()
                   Dim propertyCount As Integer = result.Properties("memberOf").Count
   
                   Dim dn As String
                   Dim equalsIndex, commaIndex
   
                   Dim propertyCounter As Integer
   
                   For propertyCounter = 0 To propertyCount - 1
                       dn = CType(result.Properties("memberOf")(propertyCounter), String)
   
                       equalsIndex = dn.IndexOf("=", 1)
                       commaIndex = dn.IndexOf(",", 1)
                       If (equalsIndex = -1) Then
                           Return Nothing
                       End If
   
                       groupNames.Append(dn.Substring((equalsIndex + 1), (commaIndex - equalsIndex) - 1))
                       groupNames.Append("|")
                   Next
   
               Catch ex As Exception
                   Throw New Exception("Error obtaining group names. " & ex.Message)
               End Try
   
               Return groupNames.ToString()
           End Function
       End Class
   End Namespace
   
   
   					

Explanation of the Code

User Authentication

User Groups

CN=...,...,DC=domain,DC=com
				

Write the Global.asax Code

1. In Solution Explorer, right-click Global.asax, and then click View Code.
2. Add the following code at the top of the code, behind the Global.asax.vb file:

   Imports System.Web.Security
   Imports System.Security.Principal
   					

3. Replace the existing empty event handler for the Application_AuthenticateRequest with the following code:

   Sub Application_AuthenticateRequest(ByVal sender As Object, ByVal e As EventArgs)
           ' Fires upon attempting to authenticate the use
           Dim cookieName As String = FormsAuthentication.FormsCookieName
           Dim authCookie As HttpCookie = Context.Request.Cookies(cookieName)
   
           If (authCookie Is Nothing) Then
               'There is no authentication cookie.
               Return
           End If
   
           Dim authTicket As FormsAuthenticationTicket = Nothing
   
           Try
               authTicket = FormsAuthentication.Decrypt(authCookie.Value)
           Catch ex As Exception
               'Write the exception to the Event Log.
               Return
           End Try
   
           If (authTicket Is Nothing) Then
               'Cookie failed to decrypt.
               Return
           End If
   
           'When the ticket was created, the UserData property was assigned a
           'pipe-delimited string of group names.
           Dim groups As String() = authTicket.UserData.Split(New Char() {"|"})
   
           'Create an Identity.
           Dim id As GenericIdentity = New GenericIdentity(authTicket.Name, "LdapAuthentication")
   
           'This principal flows throughout the request.
           Dim principal As GenericPrincipal = New GenericPrincipal(id, groups)
   
           Context.User = principal
   
       End Sub
   					

Modify the Web.config File

<?xml version="1.0" encoding="utf-8" ?>
<configuration>    
  <system.web>
    <authentication mode="Forms">
      <forms loginUrl="logon.aspx" name="adAuthCookie" timeout="60" path="/" >
      </forms>
    </authentication>	
    <authorization>	
      <deny users="?" />
      <allow users="*" />
    </authorization>	
    <identity impersonate="true" />
  </system.web>
</configuration>
				

Configure IIS for Anonymous Authentication

1. In the Internet Information Services (IIS) management console, right-click the Virtual Directory node for "FormsAuthAd".
2. Click the Properties, and then click the Directory Security Tab.
3. Click Edit under Anonymous access and authentication control.
4. Select the Anonymous Access check box.
5. Make the anonymous account for the application an account that has permission to the Active Directory.
6. Click to clear the Allow IIS To Control Password check box.

Create the Logon.aspx page

1. In Solution Explorer, right-click the project node, point to Add, and then click Add Web Form.
2. Type Logon.aspx in the Name box, and then click Open.
3. In Solution Explorer, right-click Logon.aspx, and then click View Designer.
4. Click the HTML tab in the Designer.
5. Replace the existing code with the following code:

   <%@ Page language="vb" AutoEventWireup="true" %>
   <%@ Import Namespace="FormsAuthAd.FormsAuth" %>
   <html>
   	<body>
   		<form id="Login" method="post" runat="server">
   			<asp:Label ID="Label1" Runat="server">Domain:</asp:Label>
   			<asp:TextBox ID="txtDomain" Runat="server"></asp:TextBox><br>
   			<asp:Label ID="Label2" Runat="server">Username:</asp:Label>
   			<asp:TextBox ID="txtUsername" Runat="server"></asp:TextBox><br>
   			<asp:Label ID="Label3" Runat="server">Password:</asp:Label>
   			<asp:TextBox ID="txtPassword" Runat="server" TextMode="Password"></asp:TextBox><br>
   			<asp:Button ID="btnLogin" Runat="server" Text="Login" OnClick="Login_Click"></asp:Button><br>
   			<asp:Label ID="errorLabel" Runat="server" ForeColor="#ff3300"></asp:Label><br>
   			<asp:CheckBox ID="chkPersist" Runat="server" Text="Persist Cookie" />
   		</form>
   	</body>
   </html>
   <script runat="server">
   sub Login_Click(sender as object,e as EventArgs)
     Dim adPath as String = "LDAP://DC=..,DC=.." 'Path to your LDAP directory server
     Dim adAuth as LdapAuthentication = new LdapAuthentication(adPath)
     try
       if(true = adAuth.IsAuthenticated(txtDomain.Text, txtUsername.Text, txtPassword.Text)) then
         Dim groups as string = adAuth.GetGroups()
   
         'Create the ticket, and add the groups.
         Dim isCookiePersistent as boolean = chkPersist.Checked
         Dim authTicket as FormsAuthenticationTicket = new FormsAuthenticationTicket(1, _
              txtUsername.Text,DateTime.Now, DateTime.Now.AddMinutes(60), isCookiePersistent, groups)
   	
         'Encrypt the ticket.
         Dim encryptedTicket as String = FormsAuthentication.Encrypt(authTicket)
   		
         'Create a cookie, and then add the encrypted ticket to the cookie as data.
         Dim authCookie as HttpCookie = new HttpCookie(FormsAuthentication.FormsCookieName, encryptedTicket)
   
         if(isCookiePersistent = true) then
   		authCookie.Expires = authTicket.Expiration
         end if				
         'Add the cookie to the outgoing cookies collection.
         Response.Cookies.Add(authCookie)	
   
         'You can redirect now.
         Response.Redirect(FormsAuthentication.GetRedirectUrl(txtUsername.Text, false))
       
       else
         errorLabel.Text = "Authentication did not succeed. Check user name and password."
       end if
    
     catch ex as Exception
       errorLabel.Text = "Error authenticating. " & ex.Message
     end try
   end sub
   </script>
   					

6. Modify the path in the Logon.aspx page to point to your LDAP Directory server.

• creates a FormsAuthenticationTicket object;
• encrypts the ticket;
• adds the encrypted ticket to a cookie;
• adds the cookie to the HttpResponse.Cookies collection;
• redirects the request to the URL that was originally requested.

Modify the WebForm1.aspx Page

1. In Solution Explorer, right-click WebForm1.aspx, and then click View Designer.
2. Click the HTML tab in the Designer.
3. Replace the existing code with the following code:

   <%@ Page language="vb" AutoEventWireup="true" %>
   <%@ Import Namespace="System.Security.Principal" %>
   <html>
   	<body>
   		<form id="Form1" method="post" runat="server">
   			<asp:Label ID="lblName" Runat="server" /><br>
   			<asp:Label ID="lblAuthType" Runat="server" />
   		</form>
   	</body>
   </html>
   <script runat="server">
   sub Page_Load(sender as object, e as EventArgs)
     lblName.Text = "Hello " + Context.User.Identity.Name & "."
     lblAuthType.Text = "You were authenticated using " &   Context.User.Identity.AuthenticationType & "."
   end sub
   </script>
   					

4. Save all files, and then compile the project.
5. Request the WebForm1.aspx page. Notice that you are redirected to Logon.aspx.
6. Type the logon credentials, and then click Submit. When you are redirected to WebForm1.aspx, notice that your user name appears and that LdapAuthentication is the authentication type for the Context.User.Identity.AuthenticationType property.