Create an OAuth access token for an authorized client.

        Defaults to /access_token. Invoked by client applications.

def access_token(self):
        """Create an OAuth access token for an authorized client.

        Defaults to /access_token. Invoked by client applications.
        """
        access_token = generate_token(length=self.access_token_length[1])
        token_secret = generate_token(self.secret_length)
        client_key = request.oauth.client_key
        self.save_access_token(client_key, access_token,
            request.oauth.resource_owner_key, secret=token_secret)
        return urlencode([(u'oauth_token', access_token),
                          (u'oauth_token_secret', token_secret)])