title: How to setup an SSO in PHP?
body: <p>I am currently developing my private site which consists out of many subdomains (for news/ blog etc). </p>
  
  <p>So i thought of the idea that users can login through login.domain.com. After that they should be logged in everywhere. The only problem is that im still struggling with the idea of an SSO. I dont understand how blog.domain.com can understand if the client logged in at login.domain.com since cookies/sessions are set per domain.</p>
  
  <p>Can someone briefly explain the idea (with maybe some PHP examples?). Or are there some good PHP librarys that make SSO possible (i've tried one but failed using it)?</p>