title: How does Symfony2 session fixation work?
body: <p>According to the standard 2.4 documentation, the security.yml config file allows for the following configuration option:</p>
  
  <pre><code>session_fixation_strategy: none | migrate | invalidate
  </code></pre>
  
  <p>source: <a href="http://symfony.com/doc/current/reference/configuration/security.html">http://symfony.com/doc/current/reference/configuration/security.html</a></p>
  
  <p>However, I fail to find any details in the official documentation (or elsewhere) on what this option actually does, or how it works in practice. </p>
  
  <p>So, if I set this option to either "migrate" or "invalidate", how will this affect session handling in my system? For example, if I set it to "invalidate", would this mean that a context-local session is invalidated when the user navigates to a different security context?</p>