Right, it's working, but I think I've found a few issue on the way
First the fix
The root of the issue is hosting in Azure which doesn't have the ldap library, for anyone else reading this it's a simple fix
1. Upload the php_ldap.dll (also libeay32.dll and ssleay32.dll) to a folder in the root of the website called bin
2. In the azure portal add an application setting called "PHP_Extensions" with a value of "bin/php_ldap.dll"
The problems
1. The ldap.php file is still looking for settings in the ldap table, but the management screen is saving to sitedetails, I needed to edit the table directly
2. I still cant get logging to work, I ended up putting in my own code in ldap.php to log out the debug messages