      def authenticate(self, request):
          """
          Authenticate the request and return a ``User`` instance or None. (*)
  
          This function must be overridden to be implemented.
          
          (*) The authentication context _will_ typically be a ``User`` object,
          but it need not be.  It can be any user-like object so long as the
          permissions classes on the view can handle the object and use
          it to determine if the request has the required permissions or not. 
 
</s> remove         (*) The authentication context _will_ typically be a ``User`` object,
        but it need not be.  It can be any user-like object so long as the
        permissions classes on the view can handle the object and use
        it to determine if the request has the required permissions or not. 

        This can be an important distinction if you're implementing some token
        based authentication mechanism, where the authentication context
        may be more involved than simply mapping to a ``User``.
 </s> add         .. [*] The authentication context *will* typically be a :obj:`User` object,
            but it need not be.  It can be any user-like object so long as the
            permissions classes on the view can handle the object and use
            it to determine if the request has the required permissions or not. 
    
            This can be an important distinction if you're implementing some token
            based authentication mechanism, where the authentication context
            may be more involved than simply mapping to a :obj:`User`. </s> remove ``authentication`` attribute on the ``View`` class, and listing a set of authentication classes.
 </s> add :attr:`authentication` attribute on the :class:`View` class, and listing a set of authentication classes. </s> remove Authentication behavior is provided by adding the ``AuthMixin`` class to a ``View`` .
 </s> add Authentication behavior is provided by mixing the :class:`mixins.AuthMixin` class into a :class:`View` class. </s> remove The ``authentication`` module provides a set of pluggable authentication classes.
 </s> add The :mod:`authentication` module provides a set of pluggable authentication classes.
        .. Note::
            This function must be overridden to be implemented.
      def authenticate(self, request):
          """
          Authenticate the request and return a ``User`` instance or None. (*)
  
        .. Note::
            This function must be overridden to be implemented.
          
          (*) The authentication context _will_ typically be a ``User`` object,
          but it need not be.  It can be any user-like object so long as the
          permissions classes on the view can handle the object and use
          it to determine if the request has the required permissions or not. 
keep keep keep keep replace keep keep keep keep keep
 Nicely marked up source code. 
djangorestframework/authentication.py