PHP Sessions across sub domains

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 sub2.example.com and they are not logged in, they get redirected over to auth.example.com and can log in.

sub1.example.com and sub2.example.com are two separate applications but use the same credentials.

I tried setting the following in my php.ini:

session.cookie_domain = ".example.com"

but it doesn't seem to be passing the information from one domain to the other.

[Edit]

I tried the following:

sub1.example.com/test.php

session_set_cookie_params(0, '/', '.example.com');
session_start();
print session_id() . "<br>";
$_SESSION['Regsitered'] = 1;
echo '<a href="http://auth.example.com/test.php">Change Sites</a>'

auth.example.com/test.php

session_set_cookie_params(0, '/', '.example.com');
session_start();
print session_id() . "<br>";
$_SESSION['Checked'] = 1;
print_r($_SESSION);

The session IDs are exactly the same but when I dump out the $_SESSION variable it doesn't show both keys, just whatever key I set under each domain.

I do not know if the problem still exists, but I just ran into the same problem and solved it setting a session name before calling session_set_cookie_params():

$some_name = session_name("some_name");
session_set_cookie_params(0, '/', '.example.com');
session_start();

I have changed nothing in my php.ini but now everything is working fine.

One thing which can mysteriously prevent session data being read on a subdomain, despite cookies being correctly set to .example.com is the PHP Suhosin patch. You can have everything configured correctly, as per the examples in the question, and it can just not work.

Turn the following Suhosin session settings off, and you're back in business:

suhosin.session.cryptua = Off 
suhosin.session.cryptdocroot = Off

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.

Had this exact problem - I wanted session values created on x.example.local to be available on example.local and vice-versa.

All solutions I found said to change the Session domain by using php_value session.cookie_domain .example.local in .htaccess (or via php.ini or via ini_set).

The catch was I was setting the session.cookie_domain for all subdomains (so far ok) but also for the main domain. Setting the session.cookie_domain on the main domain is apparently a no-no.

Basically the way it worked for me:

• set the session.cookie_domain for ALL SUBDOMAINS.
• don't set it for the main DOMAIN

Oh yes, please make sure the domain has a TLD (in my case .local). Http protocol doesn't allow cookies/sessions to be stored on a domain without .tld (ie localhost won't work, but stuff.localhost will).

EDIT: Also make sure you always clear your browser cookies while testing/debugging sessions across subdomains. If you don't, your browser will always send the old session cookie which probably doesn't have the correct cookie_domain set yet. The server will revive the old session and therefore you'll get false negative results. (in many posts it's mentioned to use session_name('stuff') for the exact same effect)