To use authentication from external source, follow the instructions given below:

1.  In settings.py uncomment, 
    AUTHENTICATION_BACKENDS = ('myauthentication.backend.MyBackend',) and
    AUTHENTICATION_BACKENDS = ('myauthentication.backend.MyBackend',)

2. From login.html template comment 'New User? Sign-Up' link.
   This is to be done so that user will register only from external
   application and their details will be stored in the external database.

3. In urls.py comment 'register' url pattern.