How to check if a user belongs to an AD group?

Question

At first I thought the code below works because if I have the group as "IT" it functions correctly because my username is in the IT group in active directory. What I learned is it always returns true whether I have my username in the IT group or not and if i change it to any other group I am in it returns always returns false. Any help would be appreciated.

    private void tabControl1_SelectedIndexChanged(object sender, EventArgs e)
    {
        // tab control security for admin tab
        bool admin = checkGroup("IT");

        if ((admin == true) && (tabControl1.SelectedTab == tpHistory))
        {
            tabControl1.SelectedTab = tpHistory;
        }
        else if ((admin == false) && (tabControl1.SelectedTab == tpHistory))
        {
            tabControl1.SelectedTab = tpRequests;
            MessageBox.Show("Unable to load tab. You have insufficient privileges.",
                "Access Denied", MessageBoxButtons.OK, MessageBoxIcon.Stop);
        }
    }

    // check active directory to see if user is in Marketing department group
    private static bool checkGroup(string group)
    {
        WindowsIdentity identity = WindowsIdentity.GetCurrent();
        WindowsPrincipal principal = new WindowsPrincipal(identity);
        return principal.IsInRole(group);
    }

Answer 1

Since you're on .NET 3.5 and up, you should check out the System.DirectoryServices.AccountManagement (S.DS.AM) namespace. Read all about it here:

• Managing Directory Security Principals in the .NET Framework 3.5
• MSDN docs on System.DirectoryServices.AccountManagement

Basically, you can define a domain context and easily find users and/or groups in AD:

// set up domain context
PrincipalContext ctx = new PrincipalContext(ContextType.Domain, "DOMAINNAME");

// find a user
UserPrincipal user = UserPrincipal.FindByIdentity(ctx, "SomeUserName");

// find the group in question
GroupPrincipal group = GroupPrincipal.FindByIdentity(ctx, "YourGroupNameHere");

if(user != null)
{
   // check if user is member of that group
   if (user.IsMemberOf(group))
   {
     // do something.....
   } 
}

The new S.DS.AM makes it really easy to play around with users and groups in AD!