Find if an user is part of an AD group

I have tried various ways to get the groups associated to an user of the Active Directory, but every method is quite slow.

using (PrincipalContext pc = new PrincipalContext(ContextType.Domain, domain.Text, username.Text, password.Text))
{
    UserPrincipal user = UserPrincipal.FindByIdentity(pc, IdentityType.SamAccountName, username.Text);

    if (user != null)
    {
        int userGroupTmp = 0;

        var group1Principal = GroupPrincipal.FindByIdentity(pc, IdentityType.Name, group1.Text);
        var group2Principal = GroupPrincipal.FindByIdentity(pc, IdentityType.Name, group2.Text);
        var group3Principal = GroupPrincipal.FindByIdentity(pc, IdentityType.Name, group3.Text);
        var group4Principal = GroupPrincipal.FindByIdentity(pc, IdentityType.Name, group4.Text);

        if (group1Principal != null && user.IsMemberOf(group1Principal))
        {
            userGroupTmp = 1;
        }
        else if (group2Principal != null && user.IsMemberOf(group2Principal))
        {
            userGroupTmp = 2;
        }
        else if (group3Principal != null && user.IsMemberOf(group3Principal))
        {
            userGroupTmp = 3;
        }
        else if (group4Principal != null && user.IsMemberOf(group4Principal))
        {
            userGroupTmp = 4;
        }
        // ...
    }
}

It seems that in any case it is slow. I've tried also with user.GetAuthorizationGroups() but I get the same results.

Any suggestion or different method to get the groups?

I've tried different methods and the expectation is a better performance in terms of timing.

I've solved it using another method found at this link: How to get the groups of a user in Active Directory? (c#, asp.net) The method working is the custom GetAdGroupsForUser2:

public static List<string> GetAdGroupsForUser2(string userName, string domainName = null)
{
    var result = new List<string>();

    if (userName.Contains('\\') || userName.Contains('/'))
    {
        domainName = userName.Split(new char[] { '\\', '/' })[0];
        userName = userName.Split(new char[] { '\\', '/' })[1];
    }

    using (PrincipalContext domainContext = new PrincipalContext(ContextType.Domain, domainName))
        using (UserPrincipal user = UserPrincipal.FindByIdentity(domainContext, userName))
            using (var searcher = new DirectorySearcher(new DirectoryEntry("LDAP://" + domainContext.Name)))
            {
                searcher.Filter = String.Format("(&(objectCategory=group)(member={0}))", user.DistinguishedName);
                searcher.SearchScope = SearchScope.Subtree;
                searcher.PropertiesToLoad.Add("cn");

                foreach (SearchResult entry in searcher.FindAll())
                    if (entry.Properties.Contains("cn"))
                        result.Add(entry.Properties["cn"][0].ToString());
            }

    return result;
}