keystone v2

This references the domain to use for all Identity API v2 requests
(which are not aware of domains).

A domain with this ID will be created for you by keystone-manage db_sync in migration 008.

The domain referenced by this ID cannot be deleted on the v3 API,
to prevent accidentally breaking the v2 API.

There is nothing special about this domain, other than the fact that it must
exist to order to maintain support for your v2 clients.
default_domain_id = default

A subset (or all) of domains can have their own identity driver, each with
their own partial configuration file in a domain configuration directory.
Only values specific to the domain need to be placed in the domain specific
configuration file. This feature is disabled by default; set
domain_specific_drivers_enabled to True to enable.

あう？
V2サポートのために、ドメインを省略した場合、defaultに所属する？

# Keystone Identity backend driver. (string value)
#driver=keystone.identity.backends.sql.Identity

# Maximum supported length for user passwords; decrease to
# improve performance. (integer value)
#max_password_length=4096

# Maximum number of entities that will be returned in an
# identity collection. (integer value)
#list_limit=

あう、最小文字数は？