How to Share PHP Sessions Across Multiple Subdomains?

Sharing PHP Sessions Across Subdomains

Problem:

How to establish a seamless session sharing mechanism across subdomains, ensuring that authenticated users remain logged in when navigating between these subdomains.

Background:

• Consider a setup with the following subdomains:

  • auth.example.com (authentication server)
  • sub1.example.com (application 1)
  • sub2.example.com (application 2)
• Users should be able to log in via auth.example.com and access sub1.example.com or sub2.example.com without having to log in again.

Initial Attempt with php.ini:

• Modifying the session.cookie_domain parameter in php.ini to ".example.com" did not resolve the issue.

Revised Approach:

• Set the session name before configuring cookie parameters:

  • session_name("some_name");
  • session_set_cookie_params(0, '/', '.example.com');
  • session_start();
• This modification ensures that the session name is consistent across all subdomains.

Solution Explanation:

By setting the session name explicitly, it overrides PHP's default session name generation. This ensures that the same session cookie is used across all subdomains, allowing for proper session sharing. The session.cookie_domain setting in php.ini is still necessary to ensure that the cookie is available across all subdomains.

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