python-social-auth in production (on Heroku)

Question

I'm working on a project in which I have implemented python-social-auth, and the social authentication works on localhost, but not on Heroku, where I get:

AuthCanceled at /complete/facebook/
Authentication process canceled

The complete traceback:

Environment:


Request Method: GET
Request URL: http://pin-a-voyage.herokuapp.com/complete/facebook/?redirect_state=1JFuCxsWkUZ8PQKn9oxBs8wJ5oHOZG0N&code=AQAfGiDL9NqcQSQnwVvKI9xP7SNgRPqr0554gsm-Hrdx2wWAJ17Erth8CX19Fk7R_HACaM4_r8mufA0cNZtpcg0mMDWnuz1WwaTCK_EG60JQcS55CzdA9wVPbba_sZS5V9swqyh5QVACEZugYf_W5hyP7YpEjbT82e8QxXdxN9jqGRKnYsMqwXVJxvNgoExvPXqaZx7USlcThw_ZDvzTcpq1XKCDcF0piCff4pB8vZbIry07901o8GmNz7I6SYwbCuWl4Uis4b6zENNS0BOnTYYakMJnSFJEcEO18PNZ7tzWTtUnZl9MlbRR9S2tsJy4PlQ&state=1JFuCxsWkUZ8PQKn9oxBs8wJ5oHOZG0N

Django Version: 1.8
Python Version: 2.7.6
Installed Applications:
('django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles',
 'blog',
 'custom_user',
 'django_markdown',
 'storages',
 'parsley',
 'stdimage',
 'social.apps.django_app.default')
Installed Middleware:
('django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.auth.middleware.SessionAuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware',
 'django.middleware.security.SecurityMiddleware',
 'social.apps.django_app.middleware.SocialAuthExceptionMiddleware')


Traceback:
File "/app/.heroku/python/lib/python2.7/site-packages/django/core/handlers/base.py" in get_response
  132.                     response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/views/decorators/cache.py" in _wrapped_view_func
  57.         response = view_func(request, *args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/django/views/decorators/csrf.py" in wrapped_view
  58.         return view_func(*args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/social/apps/django_app/utils.py" in wrapper
  51.             return func(request, backend, *args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/social/apps/django_app/views.py" in complete
  28.                        redirect_name=REDIRECT_FIELD_NAME, *args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/social/actions.py" in do_complete
  43.         user = backend.complete(user=user, *args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/social/backends/base.py" in complete
  41.         return self.auth_complete(*args, **kwargs)
File "/app/.heroku/python/lib/python2.7/site-packages/social/utils.py" in wrapper
  232.                 raise AuthCanceled(args[0], response=err.response)

Exception Type: AuthCanceled at /complete/facebook/
Exception Value: Authentication process canceled

I have setup SOCIAL_AUTH_LOGIN_REDIRECT_URL, SOCIAL_AUTH_LOGIN_URL, SOCIAL_AUTH_LOGIN_ERROR_URL, and obviously the secret keys from Facebook.

What could it be?