title: wp_login and is_user_logged_in
body: <p>I am developing an extension for a plugin and would like to run some code after every time a user logs in. Because I extend a plugin, I wanted to use the already written functions, which inside use <code>is_user_logged_in()</code> calls. If I register for the wp_login action and run <code>is_user_logged_in</code> in my action hook it returns false, which sounds really weird. 
  Code I was running:</p>
  
  <pre><code>add_action('wp_login', 'exhib_persist_cookies_after_login');
  
  /*
  * This method will persist the  favorite posts from the cookies just after someone logs      in.
  */
  
  function exhib_persist_cookies_after_login() {
    //Check if all the required functions are available
    if (is_user_logged_in()) { 
      error_log("persist: USER LOGGED IN"); 
    }
    else {
      error_log("persist: USER NOT LOGGED IN");
    }
  }
  </code></pre>
  
  <p>And in the log I see <em>USER NOT LOGGED IN</em>.</p>
  
  <p>Anyone has a clue why is it happening? I thought <code>is_user_logged_in</code> is checking for the auth cookie, which is according to the doc is already set before <code>wp_login</code> is getting called. </p>
  
  <p>Or anyone has an another idea what action should I register, which only fires once a user logged in and the <code>is_user_logged_in</code> returns there true?</p>