'Create access token.
:param request_id: the id of the request token, to be deleted
:type request_id: string
:param access_token_duration: duration of an access token
:type access_token_duration: string
:returns: access_token_ref'

@abc.abstractmethod
def create_access_token(self, request_id, access_token_duration):

    raise exception.NotImplemented()
