BEGIN;

ALTER TABLE rtc_task
    ADD COLUMN credential_issued_at timestamptz NOT NULL DEFAULT now(),
    ADD COLUMN credential_expires_at timestamptz NOT NULL DEFAULT (now() + interval '5 minutes');

UPDATE rtc_task rt
SET credential_issued_at = rt.created_at,
    credential_expires_at = GREATEST(c.allocation_expires_at, rt.created_at + interval '1 second')
FROM conversation c
WHERE c.id = rt.conversation_id;

ALTER TABLE rtc_task
    ADD CONSTRAINT rtc_credential_expiry_after_issue
    CHECK (credential_expires_at > credential_issued_at);

COMMIT;