Nango Webhook

Server-to-server notification from our self-hosted Nango instance that a connect session settled (success or failure). Unauthenticated by FastAPI's normal auth — identity and integrity come entirely from the HMAC signature in X-Nango-Hmac-Sha256, verified against the per- environment webhook signing key. Never trust an unsigned or mis-signed body: that would let anyone who finds this URL fabricate a connection.