Authentication
Chat apps sign in with OAuth. A custom agent can use an API key.
OAuth
Claude, ChatGPT, Gemini, Grok, and Claude Code open an OAuth prompt the first time they call a tool. Approve it once. Later calls use the same account.
The token carries three scopes. tasks:write covers the create tools, finishthis_reply, finishthis_update_task, and finishthis_cancel_task. tasks:read covers finishthis_get_tasks. account:read covers finishthis_account. A missing scope comes back as insufficient scope.
API keys
A custom agent can send Authorization: Bearer with a key that starts with ft_. Create the key in FinishThis. The secret is shown once. A key can be limited to a subset of task types.
A key that does not match returns 401. An account that is not allowed to use FinishThis returns 403.