dev.cocore.devicePair.start

Begin a device-pairing flow (OAuth 2.0 device-authorization style). Returns a `deviceId` plus a short human-typable `userCode` and the `verificationUri` where a signed-in user approves the pairing. The caller then polls `dev.cocore.devicePair.poll` until approval. The optional input lets an application (rather than a provider machine) say who it is: `appName` is shown on the approve screen, `keyName` names the minted API key so the user can recognise and revoke it, and `returnUrl` is where the approve screen sends the browser afterwards. `returnUrl` is honoured only for hosts the deployment allowlists; anything else is dropped silently, never rejected.