Login once for all domains

Hi,

I have 1 main site and 4 sub sites,

example.com

example.com/sub1/
example.com/sub2/
example.com/sub3/
example.com/sub4/

I am using the same database with different table
prefixes. I have made all sub-sites to access same user table by

define(‘CUSTOM_USER_TABLE’, ‘example_users’);
define(‘CUSTOM_USER_META_TABLE’, ‘example_usermeta’);

in wp-config.

Now I want that if a user logins in any one of the site he

must be logged-in in all other sites.

How do I do that? Please help.

I am using shared hosting on ipage.