Applications executing on phones, tablets and other client devices can be designed to authenticate with network services, but reliably identifying a client device that is not previously known to the service can be difficult. A television receiver or other trusted device that is previously known to the service, however, can act as an intermediary for initially delivering the client's identifying data to the authentication service. After the authentication service has received reliable identifying information about the client from another trusted device, the service is able to directly authenticate the client device in subsequent transactions by requesting and verifying receipt of the same secret identifier.