The name of the model class to query against. This can either be a model name (i.e.
'Users'), or a fully-namespaced class reference (i.e.
authenticating users, the magic
first() method is invoked against the model to return the
first record found when combining the conditions in the
$_scope property with the
authentication data yielded from the
Request object in
Form::check(). (Note that the
model method called is configurable using the
protected $_model = '';