Link Identity

Create an identity link: count another account as the same owner as the session user. (A sign-in provider is attached with link-provider.)

The proof is this browser session: the target must be one of the accounts signed in on it, which each entered through its own sign-in, and both the session user and the target must have proved their credential here within IDENTITY_LINK_SIGN_IN_WINDOW (#1803, #1818) — a link is symmetric, so a stale sign-in on either side would let whoever holds an old session hand that account's private contexts to another. Nothing is ever linked by an email match (#481). An id that is not in the session answers 404 whether or not such an account exists; freshness is checked only after that.

Either account may already be in a link set; the sets then merge, and every account of both is audited and sent the ACCOUNT_LINKED notice (#1875), not only the two named here.

Raises (via the global handler): 422 for the caller's own id, 404 for an account not signed in here, 403 (AUTH-305) when either account has not signed in within the window, 409 when the set would exceed its size cap.