A computer-implemented method of and a first web service system for anonymously authenticating a service user having an account associated with a first web service system are disclosed. The method is executable by a processor and comprises receiving an authentication request originating from a device of the service user, the authentication request comprising data identifying the account of the service user; generating, based on data relating to the account of the service user, a token comprising first data anonymously authenticating the service user and second data identifying an action that a second web service system is authorized to perform for the service user; storing, in a memory, at least one of the first and second data of the token; and transmitting the generated token to the second web service system. A computer-implemented method executable by a second web service system and a second web service system are also disclosed.