Access to a resource controlled by a resource server (6, 8) is provided using a validity token issued by a validation server (4). When a resource request from a user (12) is received at the resource server (6, 8), then the resource server (6, 8) determines if the resource request satisfies a policy. If the resource request satisfies the policy, then access to the resource may be permitted without confirming the validity of the validation token with the validation server (4). Conversely, if the resource request does not satisfy the policy, then validation of the validation token with the validation server (4) is performed before the access requested is permitted.