how to verify Ad group membership in php

I have a form for a user to enter username and password. then I pass those creds to a script where I want to verify the user is in a specific AD group. I have tried several gitHub adLDAP projects but none have worked. the examples in the documentation on the php manual don't even work for me (something I'm doing wrong I'm sure). below is my code and at the moment it prints out Array([count] => 0) so I'm assuming that the search isn't working and I can't figure out why. I've tried so many different "solutions" from other posts on stack but none have been successful.

$username = $_POST['username'];
$password = $_POST['password'];
$admin = 'xxxx';
$adminpass = "xxxxxx";
$domain = "";
$baseDN = "OU=ManagedUsers,DC=mydomain,DC=com";
$attr = array("displayName","sAMAccountName");
$filter ="(&(objectClass=user)(objectCategory=person)(memberof=cn=WIFI- 
$conn = ldap_connect("");
$bind = ldap_bind($conn,$admin.'@' .$domain,$adminpass);

if ($bind){//also tried ldap_search($conn,$baseDN,"memberof=CN=WIFI-Users,{$baseDN}",$attr);
  $search = ldap_search($conn,$baseDN,$filter,$attr);
  $results = ldap_get_entries($conn, $search);
  var_dump ($results);

} else 
  echo "Error in Binding";