Methods, systems, and apparatus include computer programs encoded on a computer-readable storage medium, including a method for providing content. Login credentials provided by a user are received when communicating through a first user device, and a temporal identifier is created for the user and provided to the first user device. Prior to expiration of the temporary key, login credentials provided by the user on a second different user device are received. The temporal identifier is re-created for the user and provided to the second different user device. A first request is received from the first or second different user device. The temporal identifier is stored and an identifier associated with the device. A second request is received from the other device. A device identifier for the first and second different user device are linked in association with the temporal identifier. The linking is used to respond to the second request.