Retrieve all the users in an Active Directory group using C#

Question

How do I retrieve the users in a given AD group?

Do I start by instantiating a PrincipalContext with a domain, username and password?

Answer 1

Check out this article Managing Directory Security Principals in the .NET Framework 3.5 for a great overview of what you can do with System.DirectoryServices.AccountManagement in .NET 3.5.

As for retrieving the members of a group, you do this:

// build the principal context - use the NetBIOS domain name
PrincipalContext ctx = new PrincipalContext(ContextType.Domain, "DOMAIN");

// get the group you're interested in
GroupPrincipal group = GroupPrincipal.FindByIdentity("cn=YourGroupname");

// iterate over its members
foreach(Principal p in group.Members)
{
    // do whatever you need to do to its members here            
}

Hope this helps!

Answer 2

First, find the group. Then enumerate its users using GetMembers().

using (var context = new PrincipalContext( ContextType.Domain ))
{
     using (var group = GroupPrincipal.FindByIdentity( context, "groupname" ))
     {
           var users = group.GetMembers( true ); // recursively enumerate
           ...
     }
}

Note that there is a bug, fixed in .NET 4.0, where it will fail to enumerate more than 1500 members of the group. If you have a large group you need to use an alternative method taking advantage of the older methods in System.DirectoryServices.