title: CakePHP - Access session data in Model::afterSave()
body: <p>I have <code>MyModel</code> that, whenever it is created or updated, I want to insert a row into <code>my_model_changes (MyModelChange)</code> that is a log of all changes.</p>
  
  <p>The problem is that I need <code>MyModelChange</code> to be able to save the current user's ID, so that it stores who authorised the change to <code>MyModel</code>.</p>
  
  <p>I know the model shouldn't be able to access the Auth session in MVC. However, every change to <code>MyModel</code> <em>must</em> be logged, and so I don't want to leave it up to people to remember to do this in a controller every time they modify the model, because there is a risk it will be forgotten or not done properly, in which case the log won't be complete.  Instead, I want to use <code>MyModel::afterSave()</code> so that it is automated and will always happen properly.</p>
  
  <p>So how do I get <code>MyModel</code> to find the Auth user's ID?</p>