A client device is tracked over a period of time using “refresh tokens” that are exchanged in conjunction with routine client-server communications. Each communication cycle between client and server includes a refresh token that is recorded at the server. The recorded refresh tokens are mapped to both server- and client-generated device identifiers. As communications between client and server occur, a chain of tokens, one for each communication cycle, is progressively recorded at the server. If the server receives a token that is outdated with respect to that which is otherwise expected based on the progression of the recorded chain, this suggests that the received communication was transmitted from a device that is a clone of another client device. A more robust device identification framework is therefore achieved by using a combination of device identifiers and tokens exchanged between client and server.