Zend_Auth provides an API for authentication and
includes concrete authentication adapters for common use case scenarios.
Zend_Auth is concerned only with authentication
and not with authorization. Authentication is loosely defined as
determining whether an entity actually is what it purports to be (i.e., identification),
based on some set of credentials. Authorization, the process of deciding whether to allow
an entity access to, or to perform operations upon, other entities is outside the scope of
Zend_Auth. For more information about authorization and access
control with Zend Framework, please see Zend_Acl.
Note
The Zend_Auth class implements the Singleton pattern - only one
instance of the class is available - through its static
getInstance() method. This means that using the
new operator and the clone keyword will not
work with the Zend_Auth class; use
Zend_Auth::getInstance() instead.