def METHOD_NAME(self, grant_type):
    """Validate if the client can handle the given grant_type. There are
    four grant types defined by RFC6749:
    * authorization_code
    * implicit
    * client_credentials
    * password
    For instance, there is a ``allowed_grant_types`` column in your client::
        def check_grant_type(self, grant_type):
            return grant_type in self.grant_types
    :param grant_type: the requested grant_type string.
    :return: bool
    """
    raise NotImplementedError()