Zend Framework installed. WordPress being installed in sub-folder. How do I carry over Zend user authentication to WP pages?

Solution:

Somewhere in WordPress (you likely know where since you are familiar with WordPress), you will use the following Zend Framework code:

$auth = Zend_Auth::getInstance();
if ($auth->hasIdentity()) {
  // Identity exists; get it
  $identity = $auth->getIdentity();
}

The above code is checking the session namespace and determining if an identity has been stored. If there is an identity stored, someone has authenticated and you can retrieve that authorized identity.

The above code assumes that you can load classes with the Zend_ namespace prefix from wordpress (autoload, include_path, etc.).