How to validate username and password in system.directoryservices.protocols?

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C#

security

We have a product that uses Active Directory to authenticate users and provide user and admin groups on client systems.

We recently picked up a new client who uses Novell for authentication.

What I have tried:

I have found a way to ensure that the user is a member of the users or admin groups, but I cannot seem to figure out how to modify the SearchRequest field to validate that a username and password combination are valid.

Here is how I request user information to verify they are in a given group:

private static String _certificatePath;
private static String _server;

private static SearchResponse Query(String user, String pwd, out String error)
{
    SearchResponse result = null;
    error = String.Empty;
    if (File.Exists(_certificatePath))
    {
        var identifier = new LdapDirectoryIdentifier(_server, false, false);
        try
        {
            using (var connection = new LdapConnection(identifier))
            {
                connection.SessionOptions.ProtocolVersion = 3;
                var cert = new X509Certificate();
                cert.Import(_certificatePath, null, X509KeyStorageFlags.DefaultKeySet);
                connection.ClientCertificates.Add(cert);
                connection.AuthType = AuthType.External;
                connection.AutoBind = false;
                var request = new SearchRequest()
                {
                    DistinguishedName = user, //Find this person
                    Filter = "(objectClass=*)", //The type of entry we are looking for
                    Scope = System.DirectoryServices.Protocols.SearchScope.Subtree, //We want all entries below this ou
                };
                result = (SearchResponse)connection.SendRequest(request); //Run the query and get results
            }
        } catch (Exception err)
        {
            error = String.Format("SDSP::Query {0}: {1}", err.GetType(), err.Message);
        }
    }
    else
    {
        error = "The system cannot find the Cryptography Certificate at the path specified in the Application Configuration file.";
    }
    return result;
}

How would I create a SearchRequest to validate a user / pwd combination?