PHP Sessions across sub domains

Question

I am trying to set up the following:

auth.example.com
sub1.example.com
sub2.example.com

If the user visits sub1.example.com or

Answer 1

Try using:

session.cookie_domain = "example.com"

Instead of:

session.cookie_domain = ".example.com"

Note the missing period at beginning.

Be careful using this, though, because it is not supported by all browsers.