Abstract: An apparatus is caused to store identification data of a plurality of clients in memory; cause reception of information indicating at least one identifier of a device corresponding to a client requesting access to a service; verify the identity of the client device on the basis of the received identifier; detect whether or not the identified device is authorized to communicate with the apparatus on the basis of first predetermined criteria; upon detecting that the device is authorized, cause reception of in-formation indicating at least one identifier of the client from the identified device; verify the at least one identifier of the client on the basis of the received identifier and the stored identification data; and determine, on demand, whether to issue a certificate indicating the verifications on the basis of second predetermined criteria in order to enable the client to apply the certificate in accessing the service.