Yii 2 User Extension Data Model

user.sql

CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'The KEY obviously',
  `username` varchar(20) NOT NULL DEFAULT '' COMMENT 'Login name (alnum)',
  `email` varchar(128) NOT NULL DEFAULT '' COMMENT 'User e-mail address',
  `password` varchar(128) NOT NULL DEFAULT '' COMMENT 'Secure password hash',
  `auth_client` varchar(128) NOT NULL DEFAULT '' COMMENT 'Eg. local, LDAP, GitHub, Twitter, Facebook, ...',
  `auth_key` varchar(128) NOT NULL DEFAULT '' COMMENT 'External ID',
  `activation_key` varchar(128) NOT NULL DEFAULT '' COMMENT 'Key to activate the account, sent by email',
  `superuser` int(1) NOT NULL DEFAULT '0' COMMENT '** Not sure if needed, IMHO should be implemented in another way **',
  `status` int(1) NOT NULL DEFAULT '0' COMMENT 'Eg. registered,confirmed,activated,banned',
  `registered_at` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT 'Timestamp of the registration',
  `last_login_at` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' COMMENT 'Last login time',
  PRIMARY KEY (`id`),
  UNIQUE KEY `user_username` (`username`),
  UNIQUE KEY `user_email` (`email`),
  UNIQUE KEY `user_auth` (`auth_client`, `auth_key`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

superuser is not needed and status should be either flags or be split into more columns, becuase and account can have an confirmed/unconcirmed email and at the same time the admin can ban/unban it or it could get self-locked/unlocked in case of some events like failed login attempts.

Looks good. However, I agree with @nineinchnick, since superuser field is not needed (it could be a module param).
Also, I like the suggestion regarding the snetwork table.