UUID tokens are 'deprecated in Pike' which means we should move off of them soon. Fernet tokens have some advantages.
https://docs.openstack.org/keystone/queens/admin/identity-tokens.html
https://docs.openstack.org/newton/admin-guide/identity-fernet-token-faq.html
I don't yet know what the upgrade path will look like for this, but I don't think that client code will need to be modified.