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.