-- user_identity stores the linkage between an external identity subject and a local user.
-- (provider, extern_uid) is unique across the table; provider stores the idp.uid.
-- Each local user can link at most one external account per provider.
CREATE TABLE `user_identity` (
  `id`         INT          NOT NULL AUTO_INCREMENT PRIMARY KEY,
  `user_id`    INT          NOT NULL,
  `provider`   VARCHAR(256) NOT NULL,
  `extern_uid` VARCHAR(256) NOT NULL,
  `created_ts` BIGINT       NOT NULL DEFAULT (UNIX_TIMESTAMP()),
  `updated_ts` BIGINT       NOT NULL DEFAULT (UNIX_TIMESTAMP()),
  UNIQUE (`provider`, `extern_uid`),
  UNIQUE (`user_id`, `provider`)
);

CREATE INDEX `idx_user_identity_user_id` ON `user_identity`(`user_id`);