Fix incorrect 401 vs 403 response, if lazy authentication has not taken place.

rest_framework/request.py

@@ -88,7 +88,6 @@ class Request(object):
         self._method = Empty
         self._content_type = Empty
         self._stream = Empty
-        self._authenticator = None
 
         if self.parser_context is None:
             self.parser_context = {}
@@ -206,6 +205,8 @@ class Request(object):
         Return the instance of the authentication instance class that was used
         to authenticate the request, or `None`.
         """
+        if not hasattr(self, '_authenticator'):
+            self._authenticator, self._user, self._auth = self._authenticate()
         return self._authenticator
 
     def _load_data_and_files(self):