If anyone is still following this question, the direct answer is that you need to use the decorator on the view method itself. The get and post methods defined on the APIView class just tell DRF how the actual view should behave, but the view method that the django router expects is not actually instantiated until you call LoginView.as_view().
Thus, the solution is to add the csrf_exempt decorator to urls.py. It might look as follows:
#file: urls.py
from django.conf.urls import patterns, url
from django.views.decorators.csrf import csrf_exempt
import views
urlpatterns = patterns('',
url('^login/$', csrf_exempt(views.LoginView.as_view())),
...
)
However, as Mark points out above, csrf protection is important to prevent your sessions from being hijacked. I haven’t worked with iOS myself, but I would look into using django’s cookie-based csrf tokens. You can use the ensure_csrf_cookie decorator to make django send a csrftoken cookie with a response, and your POST requests will validate as long as you include that token as an X-CSRFToken header.