Check if user is part of AD group using System.DirectoryServices.AccountManagement namespace

Question

I am trying to validate a user from SharePoint to see if a user exists within an AD group. SharePoint does not allow you to do this so I am using the:
using
System.DirectoryServices.AccountManagement;
to validate user existance within that AD group. I found the following method that allows me to validate but bombing on me:
public bool IsUserInGroup(string username, string groupname, ContextType type)
PrincipalContext context = new PrincipalContext(type);
UserPrincipal user = UserPrincipal.FindByIdentity( context, IdentityType.Name, username);
GroupPrincipal group = GroupPrincipal.FindByIdentity(context, groupname);
return user.IsMemberOf(group);
When I call my method, i get
An operations error occurred.
I read that it might be an impersination error but I have my web.config set up already with:
<
authentication mode="Windows" />
<
identity impersonate="true" />
Any suggestions from someone that has worked with that namespace on SharePoint? I just want to plainly check to see if a user is part of a certain group on AD from SharePoint.
Victor Palma

Answer 1

“An operations error occurred. “ may suggest a COMException is occurred.
I wrote an simple console application that works:
    static void Main(string [] args)
        Console .WriteLine(IsUserInGroup("Administrator" , "Domain Admins" ));
    public static bool IsUserInGroup(string username, string groupname)
        var foundUser = false ;
        var context = new PrincipalContext (ContextType .Domain, "DC" );
        var group = GroupPrincipal .FindByIdentity(context, groupname);
        if (group == null )
            context.Dispose();
            throw new Exception ("Group could not be found: " + groupname);
        // GetMembers(true) is recursive (groups-within-groups)
        foreach (var member in group.GetMembers(true ))
            try
                if (member.SamAccountName.Equals(username))
                    foundUser = true ;
                    break ;
            catch (Exception )
                // One of the members could not be retrieved, moving on...
        group.Dispose();
        context.Dispose();
        return foundUser;
Reference:
Recursive Active Directory group membership using System.DirectoryServices in .NET 3.5(http://www.lessanvaezi.com/recursive-active-directory-group-membership-using-system-directoryservices-in-net-3-5/)
Another important notice:
How to use the System.DirectoryServices namespace in ASP.NET(http://support.microsoft.com/default.aspx/kb/329986)
Keep It Simple and Stupid.