Method and system for authenticating a user comprising: transmitting a network authentication of a user, which is provided by an authentication medium, from a mobile terminal belonging to the user to a back-end server of a wireless network to carry out authentication, connecting the mobile terminal to the wireless network, starting a software application to carry out authentication with respect to an application server accessible via the wireless network, on the mobile terminal by the user, and transmitting an application authentication of the user, which is assigned to the started software application, to the application server.