Test for User Group Membership in VB.NET

Introduction

The approach shown is based on the use of Windows based authentication in conjunction with a web site configured to deny anonymous authentication and to require Windows based authentication.

The example shown would be useful on a company intranet site in which it was, for example, necessary to restrict access to certain parts of the available functionality based upon the member's role. For example, you might be working with an application that has administrative and general users; the administrative users might have additional application rights such as the ability to delete records. If one were to check for group membership in the administrator's group, the application can show or hide such functionality by getting the currently logged in user and checking whether or not that user is a group member.

There are other ways to accomplish the same sort of thing and to accomplish control level locking and the other approaches can be a bit more surgical; however, this is approach is quite easy and may be used to good effect.



Figure 1: Example Web Site showing results of a Group Membership Test

Getting Started:

In order to get started, unzip the included project and save it. Open IIS and create a virtual directory for the project and then, once it exists, right click on the web site and select "Properties". When the properties dialog box open, select the Directory Security tab and then click on the button called, "Edit" (Figure 2); this will open the "Authentication Methods" dialog box (Figure 3).



Figure 2: Edit the Anonymous Access and Authentication Settings



Figure 3: Authentication Methods

From the "Authentication Methods" dialog box, remove the check mark from "Anonymous Access" to disable the feature and check "Integrated Windows Authentication". This will force the site to require Windows Authentication which in most instances is transparent but running the application from a test instance on your local server will likely result in the display of a login dialog.

Once the settings are made, you can OK the dialog and close up the IIS control panel.



Figure 4: Solution Explorer

The solution contains a single web application project with a single page called "Default". In this case, all of the code necessary to run the demo is contained in the Default page's code behind file. 

Code: Default Page

The default page contains a simple table used to display the results of a couple of quick tests; during operation, it will look like the screen shot shown in Figure 1. The markup for the page is little more than a simple table along with a bullet list and some labels used to display the user information.
The class begins with the default imports (all of the imports are set by default): 

Imports System.Collections

Following the imports, the class declaration is shown:

 Partial Class _Default
    Inherits System.Web.UI.Page

Following the class declaration, the page load event handler is provided. The section is annotated to describe the action within Page Load:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

         ' collect the user domain and identity
        Dim arr As String() = _
            System.Web.HttpContext.Current.Request.
                LogonUserIdentity.Name.Split("\")

         ' update the display to show
         ' the captured domain and user
         If (arr.Length > 0) Then

           lblDomain.Text = arr(0).ToString()
           lblUser.Text = arr(1).ToString()

         End If

         ' clear the list of groups
       BulletedListOfGroups.Items.Clear()

         ' set the member of group label to no
         ' as a default 
         lblMemberOfGroup.Text = "NO"

        ' create an arraylist and populate
        ' it with the list of groups that
        ' the current user belongs to
        Dim al As New ArrayList()
        al = GetGroups()

         ' check to see if the user belongs
         ' to a specific group and create
         ' a list of all of the user's groups
         Dim s As String

         For Each s In al

           ' add this one to the list
            BulletedListOfGroups.Items.Add(s)

             ' check to see if the user
             ' belongs to a specific group
             If (s = "BXSWLT\SomeCustomGroup") Then

                ' change the label to show
                ' there was a match
                lblMemberOfGroup.Text = "YES"

            End If
       Next 

    End Sub

The only other code contained in the default page's code behind is used to capture a collection of groups of which the user is a member. The captured group list is used in a simple test to see if the user is a member of a particular group in the page load handler:

    Public Function GetGroups() As ArrayList

         Dim groups As New ArrayList()
         Dim group As System.Security.Principal.IdentityReference

         For Each group In 
         System.Web.HttpContext.Current.Request.LogonUserIdentity.Groups

                       groups.Add(group.Translate(GetType(
                       System.Security.Principal.NTAccount)).ToString())

        Next

        Return groups

    End Function

 End Class

Code: Web.Config

This web.config file is in the default configuration; you need only check to make sure of the type of authentication specified for the application:

<authentication mode="Windows"/>

Make sure that the authentication mode is set to Windows.

That sums up all the code necessary to make this simple check for group membership.

Summary

The article is pretty short and simple. The intent was only to show an easy approach to determining whether or not a user is a member of a group in the context of a web application running with Windows NT Authentication. The approach may be useful as a means for controlling access to the entire application or parts of the application restricted from general use.