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Marc-André Bombeck
a8b0365ca5
The cookie was the Session row's cuid. cuid is built for collision- resistant identity across distributed writers, not for unguessability — it encodes a millisecond timestamp and a process-local counter and never touches a CSPRNG. A session cookie is a bearer credential and has to be unguessable, so it now carries 32 random bytes and only the HMAC of that value is stored, matching how api_tokens and refresh_tokens already hold their secrets. Compatibility is passive, and deliberately so. A backfill cannot help: the cookie already sitting in a browser is the cuid, and nothing we generate server-side can be pushed into it — backfilling would sign everyone out at deploy. Upgrading a row in place on first use loses to the parallel requests a single page load fires: each mints its own secret, one write wins, and the losers cannot re-emit the winner's secret because only a hash is stored, so the browser can end up holding a value the row does not honour. Instead, rows minted before the column keep a NULL token_hash and stay resolvable by id, and are denied the sliding-expiry extension so they drain within the 30-day session lifetime. Every login from this release forward is on a secret at once, and an id stops authenticating the moment its row holds one. Note for operators: API_TOKEN_HMAC_KEY now also keys session cookies, so rotating it signs browser sessions out as well as invalidating tokens. It is already Core-required, so no deployment gains a new prerequisite.