I must be missing some basic thing about cookies. On localhost, when I set a cookie on server side and specify the domain explicitly as localhost (or .localhost). t
Spent a great deal of time troubleshooting this issue myself.
Using PHP, and Nothing on this page worked for me. I eventually realized in my code that the 'secure' parameter to PHP's session_set_cookie_params() was always being set to TRUE.
Since I wasn't visiting localhost with https my browser would never accept the cookie. So, I modified that portion of my code to conditionally set the 'secure' param based on $_SERVER['HTTP_HOST'] being 'localhost' or not. Working well now.
I hope this helps someone.