.net web service to validate LDAP credentials using SSL

So I'm new to the whole .net thing here, but basically what I want to do is write a web service that will take a SOAP request with user's name and password and check them against an ldap server to validate that the credentials are right. I've already done this in perl, the code is below, but I'd like to replicate it in .net to get some more exposure to it. I've been poking around with c# since I've done a good amount of java programming and it seems like they are pretty similar, but if it's easier in vb or something else I'm not opposed to that.

The main problem I'm having is actually connecting to the server itself. I've found some examples online but I'm getting confused as to what I should be passing to various methods. Here is the perl version of the web service:

authenticate.cgi

use strict;
use warnings;
use SOAP::Transport::HTTP;
SOAP::Transport::HTTP::CGI
    ->dispatch_to('Authenticate')
    ->handle;

package Authenticate;

use Net::LDAPS;
use Net::LDAP;

sub Verify{
    my ($class, $user, $pass) = @_;

    my $user_dn = "uid=$user,ou=people,o=domain";

    my $ldap = Net::LDAPS->new( 'ldap.domain.com', port => '636' ) or die "$@";

    my $mesg = $ldap->bind($user_dn, password => $pass);

    return $mesg->error if $mesg->is_error;

    return "Successful authentication for user '$user'";
}

What i've been messing with in c# is the following (I might have unnecessary includes, i've been messing with a bunch of things):

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Services;
using System.DirectoryServices;
using System.DirectoryServices.Protocols;
using System.Net;


/// <summary>
/// Summary description for WebService
/// </summary>
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
// To allow this Web Service to be called from script, using ASP.NET AJAX, uncomment     the following line. 
// [System.Web.Script.Services.ScriptService]
public class WebService : System.Web.Services.WebService {

    public WebService () {

        //Uncomment the following line if using designed components 
        //InitializeComponent(); 
    }

    [WebMethod]
    public string Authenticate(string username, string pwd) {
        string domain = "LDAP://ldap.domain.com:636";
        string domainAndUsername = domain + @"\" + username;
        string path = domain + @"/ou=people,o=domain";
        string filterAttribute;
        DirectoryEntry entry = new DirectoryEntry(path, domainAndUsername, pwd);

        try
        {
            //Bind to the native AdsObject to force authentication.
            object obj = entry.NativeObject;

            DirectorySearcher search = new DirectorySearcher(entry);

            search.Filter = "(SAMAccountName=" + username + ")";
            search.PropertiesToLoad.Add("cn");
            SearchResult result = search.FindOne();

            if (null == result)
            {
                return "false";
            }

            //Update the new path to the user in the directory.
            path = result.Path;
            filterAttribute = (string)result.Properties["cn"][0];
        }
        catch (Exception ex)
        {
            throw new Exception("Error authenticating user. " + ex.Message);
        }

        return "true";
    }

}

This has been resulting in the error

System.Exception: Error authenticating user. The server is not operational.

I feel like I am just specifying the path wrong somewhere or something like that, but I can't seem to figure it out.