[keystone] failed auth takes a while

Hi, I am using Keystone 17.0.0 with Ussuri. When issue a request by openstack cli (eg. network list) with wrong password, it takes 1+ minute to get auth failure 401 back. After correct the password, for the first request, it still takes 1+ minute to return success. After that, all following request is as fast as usual, around 1s. "openstack user password set" also takes that much time to return success. Any clues? Thanks! Tony