Methods, systems, and apparatus, including computer programs encoded on computer storage media, to authenticate mobile traffic. One of the methods includes receiving a first request for a strategy from a client device over a network. The method includes providing a current strategy to the client device, the current strategy including characteristics used to authenticate requests from the client device based on the inclusion of the characteristics in the request. The method includes receiving, from the client device, a second request for access to a processing system. The method includes validating the second request according to one or more strategies, including the current strategy. The method also includes forwarding the second request to the processing system based on the validation.