'Adds an access token for the given user.
Args:
user_id (str): The user ID.
token (str): The new access token to add.
device_id (str): ID of the device to associate with the access
token
Raises:
StoreError if there was a problem adding this.'

@defer.inlineCallbacks
def add_access_token_to_user(self, user_id, token, device_id=None):

    next_id = self._access_tokens_id_gen.get_next()
    (yield self._simple_insert('access_tokens', {'id': next_id, 'user_id': user_id, 'token': token, 'device_id': device_id}, desc='add_access_token_to_user'))
