LDAP: How to add a new user to a group inside an OU

Question

I have some code using DirectoryEntry to manipulate the local Active Directory via LDAP. Currently I find a specific OU, add a user to it, update the properties of the user and then commit all changes:

DirectoryEntry ldapRoot = new DirectoryEntry(ldapString, user, password);
DirectoryEntry userGroup = ldapRoot.Children.Find("OU=OUGroup");
DirectoryEntry newUser = userGroup.Children.Add("CN=" + userName, "user");
newUser.Properties["displayName"].Value = displayName;

...

newUser.CommitChanges();
userGroup.Close();
ldapRoot.Close();

ldapString is something akin to LDAP:\\DC=company,DC=local, basically it's just fetching the root entry.

I change several Properties, but it's all working fine. However, I have another OU called SharePoint_Groups, which has a group inside called Internal. I want to add the new user as a member of this group, but I'm at a loss of how to do it. I tried the following:

DirectoryEntry spGroup = ldapRoot.Children.Find("OU=Sharepoint_Groups");
DirectoryEntry internal = spGroup.Children.Find("CN=Internal");

It does not work and I am not sure how I should address Internal - is CN= correct or should I use some other specification?

And, once I have the correct group, how do I add the existing user to it?

Thanks in advance

Solution

Basically, to add a user to an existing group, you need to bind to that group and update it's member property, using the user's fully qualified distinguished name:

DirectoryEntry deGroup = new DirectoryEntry("LDAP://CN=Internal,OU=Sharepoint_Groups,DC=Company,DC=local");

string userDN = newUser.Properties["distinguishedName"][0].ToString();

deGroup.Properties["member"].Add(userDN);
deGroup.CommitChanges();

A great resource for stuff like this is the CodeProject article How to do just about everything in Active Directory using C# - lots of useful code samples!