Missing configuration keys for 'webapp2_extras.sessions': ['secret_key']

I added webapp2 sessions to my project on appengine which uses webapp2 for request handling and django for templates.

Following this page, I added the following to my script

import webapp2

from webapp2_extras import sessions

class BaseHandler(webapp2.RequestHandler):
    def dispatch(self):
        # Get a session store for this request.
        self.session_store = sessions.get_store(request=self.request)

        try:
            # Dispatch the request.
            webapp2.RequestHandler.dispatch(self)
        finally:
            # Save all sessions.
            self.session_store.save_sessions(self.response)

    @webapp2.cached_property
    def session(self):
        # Returns a session using the default cookie key.
        return self.session_store.get_session()

config = {}
config['webapp2_extras.sessions'] = {
    'secret_key': 'my-super-secret-key',
}

However, now I get the following error

Traceback (most recent call last):
  File "/home/user/google_appengine/lib/webapp2/webapp2.py", line 1536, in __call__
    rv = self.handle_exception(request, response, e)
  File "/home/user/google_appengine/lib/webapp2/webapp2.py", line 1530, in __call__
    rv = self.router.dispatch(request, response)
  File "/home/user/google_appengine/lib/webapp2/webapp2.py", line 1278, in default_dispatcher
    return route.handler_adapter(request, response)
  File "/home/user/google_appengine/lib/webapp2/webapp2.py", line 1102, in __call__
    return handler.dispatch()
  File "/home/user/sites/project2n/main.py", line 804, in dispatch
    self.session_store = sessions.get_store(request=self.request)
  File "/home/user/google_appengine/lib/webapp2/webapp2_extras/sessions.py", line 454, in get_store
    store = request.registry[key] = factory(request)
  File "/home/user/google_appengine/lib/webapp2/webapp2_extras/sessions.py", line 308, in __init__
    required_keys=('secret_key',))
  File "/home/user/google_appengine/lib/webapp2/webapp2.py", line 1361, in load_config
    self._validate_required(key, config, required_keys)
  File "/home/user/google_appengine/lib/webapp2/webapp2.py", line 1375, in _validate_required
    'Missing configuration keys for %r: %r.' % (key, missing))
Exception: Missing configuration keys for 'webapp2_extras.sessions': ['secret_key']

I have set the secret key, using config. I am not using anything else for sessions. The other imports are

import os,sys, string, time, sha, Cookie
from django.template import Context, Template
from django.template.loader import get_template

You need to include this config somewhere, such as in the WSGI app you create:

app = webapp2.WSGIApplication([('/path', MyHandler)],
                              config=config,
                              debug=True)