Hello Pete,
The auth_token middleware is responsible for generating and validating these tokens using a shared secret key. The middleware also caches these tokens in memory so that they can be reused by other services without contacting Keystone again.
The memcached_servers config option can be set in different places depending on the OpenStack service. For example, for nova, it can be set in the [nova] section of the devstack configuration file.
For Cinder, it can be set in the [cinder] section of the devstack configuration file.. However, this option does not affect how Cinder or Nova use memcached internally. They still rely on authtoken middleware to handle authentication and authorization
I hope it helps your question.
Kerem ÇELİKER Head of Cloud Architecture linkedin.com/in/keremceliker/