single signon codeigniter with csrf

Hi all codeigniter gurus i have some questions about the logic and ideas of how to use a single sign on on codeigniter with csrf?

for example i have a site which is called test.com when i login on this all its subdomain will login as well

payroll.test.com
members.test.com
profiles.test.com

anybody have ideas on how do i implement this on codeigniter? i have tried using an ajax to submit as well but its not working it keeps at 500 i have disable its csrf to false its not working as well any thoughts?