The application describes an attestation system (705, 707, 710) in a cloud computing environment. The authorization system is configured to allow a plurality of users (701a-d) and applications (702, 706, 708, 709) of the cloud computing environment to issue attestations regarding attributes of other users and applications. The authorization system is also configured to control access to said attestations and to allow a plurality of users and applications of the cloud computing environment to query the authorization system to determine whether a specified user or application has a specified attribute. Methods of controlling access to resources in a cloud computing environment and also of providing secure attestations are also described.