title: How do I set 'current_user' even though a user is not logged in? - Rails 3
body: <p>I am using Devise for authentication, and when someone visits a specific URL (with specific params in the URL), I would like to set the 'current_user' to a specific value from the db.</p>
  
  <p>How do I do that ?</p>
  
  <p>Also, will I have to make sure all the validation requirements are satisfied ? E.g., my user model has:</p>
  
  <pre><code>validates_presence_of :username, :email
  </code></pre>
  
  <p>If I set the current_user, would I have to set both the :username &amp; :email, or can I just do one or the other ?</p>