Returns a dictionary mapping cookie names to their values.

def cookies(self):
        """Returns a dictionary mapping cookie names to their values."""
        if self._cookies is None:
            c = SimpleCookie(self.environ.get('HTTP_COOKIE'))
            self._cookies = dict([
                (k.decode('utf-8'), v.value.decode('utf-8'))
                for k, v in c.items()
            ])
        return self._cookies