Authentication method and devices

A method for authenticating an entity at a first data resource, the method comprising the steps of: sending a first request token from the entity ( 100 ) to a token distribution unit ( 20 ) to request a first one-way authentication token, the first request token being a function of authentication information provided by the entity ( 100 ); sending the first one-way authentication token from the token distribution unit ( 20 ) to the entity ( 100 ); sending the first one-way authentication token from the entity ( 100 ) to the first data resource ( 200 ) to authenticate the entity ( 100 ) at the first data resource ( 200 ); sending the first one-way authentication token from the first data resource ( 200 ) to the token distribution unit ( 20 ) to validate the first one-way token; and invalidating the first one-way token.