For a recent project I recently I have been using appengine's cron feature to aggregate data and perform maintenance tasks. However, since cron is a simple web request, if a user accesses that url then the cron job will run. In order to prevent normal users from being able to run cron jobs I created a decorator that specifies a view as cron only.

This decorator is for use with the kay framework but it should be easy to port to your application.

def cron_only(func):
    from werkzeug import Response
    def inner(request, *args, **kwargs):
        import os
        from kay.conf import settings
        if not ('SERVER_SOFTWARE' in os.environ and \
            os.environ['SERVER_SOFTWARE'].startswith('Dev') and \
            settings.DEBUG) and \
           not request.headers.get("X-AppEngine-Cron") == "true":
            return Response("Cron only", status=403)
        return func(request, *args, **kwargs)
    return inner