An authentication method for use by application servers on networks to authenticate users of the applications is provided. In the method, an application server receives authentication data from the user. The application server determines the type of authentication data received from the user and determines a suitable verification server. The received authentication data is sent together with the identification data of the user to a verification server. The verification server verifies whether the sent authentication data is the authentication data of the user designated by the sent identification data. The verification server notifies the application server of the verification result and, on the basis of the returned verification result, the application server authenticates the user.