Create an OAuth request token for a valid client request.

        Defaults to /request_token. Invoked by client applications.

def request_token(self):
        """Create an OAuth request token for a valid client request.

        Defaults to /request_token. Invoked by client applications.
        """
        client_key = request.oauth.client_key
        realm = request.oauth.realm
        # TODO: fallback on default realm?
        callback = request.oauth.callback_uri
        request_token = generate_token(length=self.request_token_length[1])
        token_secret = generate_token(length=self.secret_length)
        self.save_request_token(client_key, request_token, callback,
            realm=realm, secret=token_secret)
        return urlencode([(u'oauth_token', request_token),
                          (u'oauth_token_secret', token_secret),
                          (u'oauth_callback_confirmed', u'true')])