title: Set RestAngular default request parameters after login
body: <p>I'm hitting an API which requires all authenticated actions to include an auth token in the request, however, I do not have the auth token until I login.</p>
  
  <p>I've only seen examples of setting default request parameters in Restangular in <code>app.config</code>.
  Is it possible to set this until after the user has logged in and <code>User.auth_token</code> is set?</p>
  
  <p>So basically instead of:</p>
  
  <pre><code>app.config(function(RestangularProvider) {
      RestangularProvider.setDefaultRequestParams({
          auth_token: 'thisistheauthenticationtoken'
      });
  });
  </code></pre>
  
  <p>I need:</p>
  
  <pre><code>app.config(function(RestangularProvider) {
      RestangularProvider.setDefaultRequestParams({
          auth_token: User.auth_token
      });
  });
  </code></pre>