public string addUserToGroup(string userDN, string groupDN)
{
    try
    {
        DirectoryEntry de = new DirectoryEntry("LDAP://localhost:389/" + groupDN);
        de.Username = "myUsername";
        de.Password = "myPassword";
        de.Properties["member"].Add(userDN);
        de.CommitChanges();
        de.Close();
        //return true;
        return "yes";
    }

CN=sandbox,CN=testApp1,DC=ITOrg
CN=sandbox,CN=testApp2,DC=ITOrg  .. etc

CN=1@test.com,CN=People,CN=sandbox,DC=ITOrg

CN=Readers,CN=Roles,CN=sandbox,CN=testApp1,DC=ITOrg