Validate and Search against Active Directory

UsersRepository.cs

namespace api_v1_csharp.Models.ldap
{
    using System;
    using System.DirectoryServices;
    using System.DirectoryServices.ActiveDirectory;
    using System.DirectoryServices.AccountManagement;
    using System.Collections.Generic;

    public class UsersRepository : IUsersRepository
    {
        public bool ValidateCredentials(string username, string password)
        {
            using (PrincipalContext pc = new PrincipalContext(ContextType.Domain))
            {
                return pc.ValidateCredentials(username, password);
            }
        }

        public User Get(string username)
        {
            ActiveDirectorySite adSite = ActiveDirectorySite.GetComputerSite();
            Forest forest = Forest.GetCurrentForest();
            GlobalCatalog globalCat = forest.FindGlobalCatalog(adSite.Name);
            DirectorySearcher dirSearcher = globalCat.GetDirectorySearcher();
            dirSearcher.CacheResults = false;
            dirSearcher.ReferralChasing = ReferralChasingOption.All;
            dirSearcher.SearchScope = SearchScope.Subtree;
            dirSearcher.Filter = String.Format("(&(objectcategory=person)(samaccountname={0}))", username);

            try
            {
                using (DirectoryEntry entry = dirSearcher.FindOne().GetDirectoryEntry())
                {
                    User user = new User();
                    user.samaccountname = username;
                    user.distinguishedname = entry.Properties["distinguishedname"][0].ToString();
                    user.displayname = entry.Properties["displayname"][0].ToString();
                    user.mail = entry.Properties["mail"][0].ToString();
                    user.memberOf = "";

                    // some students don't have these properties ie. mcdowe623
                    try
                    {
                        user.givenname = entry.Properties["givenname"][0].ToString();
                        user.sn = entry.Properties["sn"][0].ToString();
                    }
                    catch (Exception)
                    {
                        user.givenname = "";
                        user.sn = "";
                    }

                    string cn;
                    user.groups = new List<string>();
                    foreach (string group in entry.Properties["memberOf"])
                    {
                        // Client applications already depend on 'memberOf'
                        user.memberOf += group.ToString() + ";";

                        cn = group.ToString().Split(',')[0].Split('=')[1];
                        user.groups.Add(cn);
                    }

                    return user;
                }
            }
            catch (Exception)
            {
                return null;
            }
        }
    }
}